Anthropocene 8 (2014) 39–45

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Anthropocene

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Assessing change in floodplain condition in the Murray Darling Basin, Australia

Peter Gell a,*, Michael Reid b a Water Research Network, Federation University Australia, Ballarat, Victoria, Australia b Riverine Landscapes Research Laboratory, University of New England, Armidale, NSW, Australia

ARTICLE INFO ABSTRACT

Article history: Lowland Australian rivers and floodplains have been affected by agriculture and flow regulation for more Received 31 July 2014 than a century. Our capacity to understand the complex causes of ecosystem change is limited by the lack Received in revised form 10 December 2014 of historical records of ecosystem condition. Records of change over this critical period are available Accepted 11 December 2014 through analysis of sedimentary records. These provide benchmarks of the range of natural conditions Available online 18 December 2014 and, by providing a long time series of conditions, trends and trajectories of change. Over recent decades, 51 sediment records from billabongs and lagoons throughout the southern Murray Darling Basin have Keywords: been subject to palaeoecological analysis. The picture that emerges from this synthesis is that ecosystems have undergone substantial ecological change in response to human activities. Diatom Salinity assemblages preserved in wetland sediments attest to salinisation in 34% of sites and increased nutrient Regime shift concentrations in 48%. More extensive is the impact of increased sediment flux with evidence for Sediments increased sedimentation rate, turbidity or macrophyte loss in 80% of sites. Intriguing differences exist in Nutrients the timing and nature of change experienced by aquatic ecosystems in different parts of the Basin. These patterns of ecosystem response suggest underlying differences in the resilience of these ecosystems to different anthropogenic stressors, which may result from contrasting hydrologic, geomorphologic and climatic contexts. This systematic compilation of the palaeoecological evidence of change in the aquatic ecosystems of the Basin sheds light on what are the principal drivers of change across the region and provides guidance as to how these systems can be best restored. ß 2014 Elsevier Ltd. All rights reserved.

Introduction rivers’ waters were sought for irrigation agriculture from as early as 1888. When variable river flows brought calls for river The Murray Darling Basin is Australia’s largest, and among the regulation to ensure passage, the commissioning of weirs from twenty largest in the world, spanning 1.06 Â 106 km2. Human 1922 most advantaged the irrigators, with river transport having presence in the river basin has considerable antiquity with largely succumbed to that on land. By 1936 much of the lower evidence for occupation of Lake Mungo dated to before 42,000 River Murray was regulated and significant additions to the years B.P. (Bowler et al., 2003). While the junction of the Murray reservoir system were marked by the commissioning of the Hume and Darling Rivers hosted a relatively large population of Weir (1520 GL; upgraded to 3040 GL in 1961) in 1936 and (Pardoe, 1998), the impact of human Dartmouth Dam (3800 GL) in 1980 (Ogden, 2000). populations increased substantially after the arrival of European The Murray Darling Basin extends from sub-tropical zones in settlers from the 19th century. From early in settlement the southern Queensland to temperate climates in the south. Its main catchment was used extensively for sheep and cattle grazing and watershed is the elevated, alpine to sub-alpine zones in the south- the main rivers were a focus for travel owing to the difficulty of east associated with the Great Dividing Range. To the west the traversing the land. For navigation trees were cut for firing engines effect of continentality, and prevailing sub-tropical high pressure and channels were cleared of woody debris. Early on stocking rates cells, ensures a drier climate. Here, low in the catchment, the main of sheep and cattle were high and impacts intense, particularly river channels pass through semi-arid, and even arid, climate along stock routes where animals were driven to markets. The zones. So, the main runoff is driven by cool season rainfall in the south-east, followed by snow melt, yet the northern parts of the catchment can receive warm season rainfall. Ultimately, river flow

* Corresponding author. is impacted by high evaporation rates in the dry, western zone limiting the volumes that pass through the outlet to the sea in http://dx.doi.org/10.1016/j.ancene.2014.12.002 2213-3054/ß 2014 Elsevier Ltd. All rights reserved. 40 P. Gell, M. Reid / Anthropocene 8 (2014) 39–45

South Australia. In all, this climatic context ensures that the region magnitude of the influence of these drivers of change can be hosts the most variable runoff on Earth (McMahon and Finlayson, documented. 1992). Despite this, the Basin hosts sixteen wetlands registered under the Ramsar convention on wetlands of international Sediment records significance. River regulation and a very high water reserve were responses to a highly variable climate. The region is subject to the Long term records of change exist where the biological remains cycles of dry and wet associated with the El Nin˜o Southern of organisms are buried with sediments in still water environ- Oscillation, as well as the Indian Ocean Dipole, which can bring ments. Continuous sediment records that contain this evidence are significant drought phases and extensive floods. Most notable are more likely in sites which are perennially covered in water. The the Federation Drought (1907), the World War II drought and the climatic diversity of the Basin dictates that some areas are more recent Millennium Drought (1997–2009), considered the longest humid than others and the high climatic and runoff variability and deepest dry phase in European history (Gergis et al., 2012). The ensures that basins in many areas are not always filled with water. region is also impacted by multi-decadal climate variability So, sites which provide continuous records are focussed in the associated with the Pacific Decadal Oscillation with significant humid upper catchments and along the main channels where wet phases (1845–1898; 1946–1976), deemed flood-dominated overbank flows regularly refill wetlands. Critically too, many regimes, and extended dry phases (1898–1946; 1997–?) under intermittent floodplain wetlands have become permanent, their drought-dominated regimes (Warner, 1987). Notably, La Nin˜a water level linked to the height of the weir pool behind a nearby ensured that the early 20th century drought-dominated regime lock, and so provide sediment records mostly over the last century. was interrupted by the 1917 flood. One could speculate that, Central to the reconstruction of a long term history from similarly, the 2010–2011 floods were mere interruptions of an sediment is the establishment of chronology. As dead carbon can extended drought dominated regime that commenced in 1997, be exposed to air and degraded or metabolised radiocarbon particularly given rainfall deficits have continued across the region techniques are not straightforward, particularly where there are since 2011. Drying is likely into the future with south-eastern geological sources of old carbon. Also, 210Pb approaches to date Australia identified as a global climate hotspot at risk of substantial sediments are best where the proportion of aerial input of fine declines in wet (cool) season rainfall (Giorgi, 2006). sediment is highest. Clearly, floodplain systems naturally receive The waterways of the Murray Darling Basin are recognised as river borne sediments, episodically, creating challenges in being in a degraded condition (Norris et al., 2002; Davies et al., developing depth-age models in sediment sequences (Gell et al., 2012). Only the remote, unregulated streams of the arid north- 2005a). Further, luminescence dating relies on a known dosimetry west are considered in good ecological condition with the (Gell et al., 2007) and this varies if a lake is wet or dry. So, the remaining, intensively used systems considered degraded or even establishment of time lines, especially at around the time of known severely degraded. This state is closely associated with the level of first impact by European people from the 1830s, is challenging and abstraction and diversion of river flow, largely for irrigation few confidently dated sequences exist. Nevertheless, the use of a agriculture. Much infrastructure was funded to significantly suite of dating techniques, including exotic pollen, provides for increase water allocations through the flood dominated regime generalised chronologies which enable attribution of human of the post WW II period. This has left water users, and the impact; albeit not so precisely in time. environment, highly vulnerable to the recent drought, and in Traditionally, in Australia at least, fossil pollen was the main particular, a drought-dominated regime should the ‘drought’ biological indicator extracted from sediments. This focus was to persist beyond the recent La Nin˜a phase. In response to this water examine vegetation responses to long term climate cycles and was stress the local authority has implemented a highly contested infrequently applied to reconstructing the impact of industrialised Murray Basin Plan that dictates that 3200 GL of water will be people, particularly along rivers where records were considered returned to the environment to restore its health. Depending on too shallow to be of great interest. Over the last 25 years Australian whether this water is redeemed through the purchase of water palaeoecology has increasingly utilised fossil diatoms as an rights, or through water efficiency infrastructure, the provision of indicator (e.g. Gell et al., 1994). Diatoms reflect water quality this environmental allocation will come at a cost of between $5.5B and so have better enabled the provision of evidence of human and $27.5B AUD (Wittwer and Dixon, 2013). impact on aquatic systems. In concert with radiometric dating of However, the provision of water is likely only one of the drivers sedimentation rates, and other preserved indicators such as of the degraded condition of the Basin’s aquatic systems with the cladocera and plant macrofossils, changes in the salinity, nutrient increased flux of salt, sediments and nutrients strongly implicated status, turbidity, acidity and sedimentation of wetlands can be in the changing waterway condition. Little is known of the past gauged. variation in these drivers of change with water quality monitoring In this study we review, and synthesise, records of wetland programmes commencing only from the mid-1900s. This change in the southern Murray Basin derived from published and instrumental data is pre-dated by the clearance of vegetation other sources. We focus on the evidence from preserved diatom from the catchment, the initiation of intensive cropping, the sequences as these are the most comprehensive. Commonly widespread application of irrigation water, the regulation of flow training sets are used to calibrate assemblages to water quality to and the running of many million head of grazing stock. quantitatively reconstruct a parameter over time. Due to the Regionalwatertablesandextensiveerosionwasnotedbythe variability in the source of water to floodplain wetlands this has 1930s. So, reference to the available data will not reveal the only rarely been attempted here (e.g. Gell et al., 2007). Inferences impact of these early drivers of waterway change. Evidence for of water quality change (salinity and nutrients) are inferred these changes is evident, however, in the natural archives of the qualitatively based on known training sets and index systems biological elements of wetlands and rivers that are preserved in developed in Australia (Gell, 1997; Tibby and Reid, 2004; Philibert continuous sediment sequences. These records of change have et al., 2006; Chessman et al., 2007) and elsewhere (e.g. Van Dam been a focus of recent research and the condition of many et al., 1994). Inferences for increased sediment load are derived wetlands, relative to their unimpacted state, has now been from the chronology used in each study, which is mostly based on revealed (e.g. Thoms et al., 1999; Gell et al., 2005a,b; Fluin et al., 210Pb-based radiometric dating, usually supported by the first 2007, 2010; Reid et al., 2007). This synthesis of 51 such records evidence for exotic pollen (e.g. Pinus), often using a locally reveals changes at a sub-catchment scale and so the timing and developed technique (Ogden, 2000). Changes in the autotrophic P. Gell, M. Reid / Anthropocene 8 (2014) 39–45 41

Table 1 Summary of changes deduced from fossil diatom and cladoceran assemblages in records from Murray Basin wetlands (S, salinity; N, nutrients; T, turbidity; SR, sedimentation rates; A, acidity).

Site Section Core depth (cm) Estimated age (yrs) Change Source

39. Ajax Achilles Lwr Murray 250 2200 T Fluin and Gell (in preparation) 47. Alexandrina nth Murray estuary 85 7000 N, T Reid et al. (2002), Gell et al. (2005b), Fluin et al. (2007) 48. Alexandrina sth Murray estuary 500 7000 N, T Gell et al. (2005b), Fluin et al. (2007) 9. Balranald Weir Murrumbidgee 100 100 S, N Gell and Little (2006) 2. Berry Jerry Murrumbidgee 150 >200 S, N, SR Gell and Little (2006) 10. Billabong 9 Upper Murray 200 >200 T, SR Ogden (2000) 16. Billabong 21 Ovens 130 >200 T Ogden (2000) 17. Billabong 23 Ovens 150 3800 T Ogden (2000) 18. Billabong 25 Ovens 150 >200 T Ogden (2000) 19. Billabong 32 Upper Murray 200 2900 T, SR Ogden (2000) 20. Billabong 38 Upper Murray 260 T, SR Ogden (2000), Reid et al. (2002) 1. Boman Murrumbidgee 85 <100 S, N, SR Gell and Little (2006) 42. Brenda Park Lwr Murray 140 >100 N, T Fluin and Gell (in preparation) 21. Callamondah 2 Goulburn 210 >3000 N, alkalinity Thoms et al. (1999), Reid (2002) 22. Callamondah 1 Goulburn 125 >3000 N, alkalinity Thoms et al. (1999), Reid (2002), Gell et al. (2005b) 4. Coonoocoocabil Murrumbidgee 115 100 S, N, SR Gell and Little (2006) 49. Coorong ntha Murray Estuary 87–594 7000 S, N, T, SR Fluin et al. (2007), Gell (in press) 50. Coorong stha Murray Estuary 66–800 2000 S, N, T, SR Gell (in press) 28. Cullulleraine Sunraysia, Vic 35 <100 N, T Reid et al. (2002), Fluin et al. (2010) 51. Goolwa Barrage Murray estuary 210 800 Fresher Fluin and Gell (in preparation) 5. Gooragool Murrumbidgee 70 >200 S, N Gell and Little (2006) 37. Gurra Nth , SA 50 <80 S, N, T Fluin and Gell (in preparation) 38. Gurra Sth Riverland, SA 40 <80 T Fluin and Gell (in preparation) 11. Hogans 1 Upper Murray 260 1500 T, SR Ogden (2000), Reid et al. (2007) 12. Hogans 2 Upper Murray 170 1000 T Reid et al. (2007), Reid (2008) 13. Hogans 3 Upper Murray 160 200 T Reid (2008) 6. Homestead Murrumbidgee 35 100 S, N, SR Gell and Little (2006) 25. Hopcrofts Murray d/s Murrumbidgee 240 1000 SR, T Gell et al. (2005b) 14. Iona 1 Upper Murray 200 1000 T Reid (2008) 15. Iona 2 Upper Murray 260 3500 T Reid (2008) 24. Junction Park Mid Murray 180 1950 N, T Adamson (2002) 23. Longmore Gunbower, Vic 94 >100 T, SR Grundell and Gell (unpublished) 40. Loveday Riverland, SA 125 800 S, N, SR, A Gell et al. (2007) 41. Luna Riverland SA 45 250 S, N, SR Gell et al. (2007), Gell (2010) 27. Kings Murray u/s Darling 130 <150 T, SR Kattel et al. (in press) 31. Martin’s Bend Riverland, SA 60 <100 S, A Gell (2010) 7. McKenna’s Murrumbidgee 40 100 S, N, SR Gell and Little (2006) 34. Mundic Riverland, SA 300 3000 T, SR Gell (2012) 8. Russell’s Murrumbidgee 160 >300 T Reid (unpublished) 26. Psyche Bend Sunraysia, Vic 150 <150 S, N, A Silva and Gell (unpublished) 29. Moorna Lwr Murray, NSW 60 <100 S, N, T, SR Heinitz and Gell (unpublished) 46. Muroondi Lwr Murray, SA 1400 5000 N, SR Gell et al. (2005b), Fluin and Gell (in preparation) 32. Paringa Riverland, SA 130 >100 N, T Fluin and Gell (in preparation) 36. Pikes Riverland, SA 200 >100 N, T, SR Gell et al. (2006), Fluin and Gell (in preparation) 33. Ral Ral Riverland, SA 81 80 N, T, SR Gell et al. (2006), Fluin and Gell (in preparation) 35. Tanyaka Riverland, SA 280 2000 T, SR Fluin and Gell (in preparation) 30. Tareena Lwr Murray, NSW 460 5000 S, SR Gell et al. (2005a,b) 43. Scott Ck Lwr Murray, SA 300 >200 SR Fluin and Gell (in preparation) 44. Sinclairs Lwr Murray, SA 90 <100 N, T, SR Gell (2010), Grundell et al. (2013) 45. Swanport Lwr Murray, SA 700 >100 SR Gell (unpublished) 3. Yanco Weir Murrumbidgee 55 100 S, N, T, SR Gell and Little (2006)

a Cores were taken from 15 sites across each Coorong lagoon. All changes are increases except where noted e.g. fresher. Number sequence is from tributaries to mouth (east–west). community due to increased turbidity are inferred from multiple occurred to the condition of the Basin’s wetlands since European sources of evidence including changes in epiphytic and planktonic settlement. Also evident is the variable sensitivity of wetlands to diatoms, especially those in the Fragilariaceae, changes in the stressors with some sites (e.g. Hogan’s Billabong) switching macrofossil remains where available, and physical evidence for abruptly to a phytoplankton state, while in others (e.g. Sinclairs erosional inputs from magnetic susceptibility or particle size Flat) the diatom assemblages change from benthic forms to analyses (e.g. Reid et al., 2007). tychoplanktonic, but over the full extent of the record which covers An updated synthesis of all available palaeolimnological nearly 100 years. records reported across the southern Murray Darling Basin is Among the most striking changes to the diatom flora of the provided in Table 1 and their locations are shown in Fig. 1. Together wetlands of the southern Murray Darling Basin is the widespread they provide evidence for widespread wetland salinisation and shift to assemblages dominated by small, tychoplanktonic diatom eutrophication with increases in diatom-inferred salinity and forms within the Fragilariaceae. Many records attest to the recent nutrient concentrations revealed in 34% and 48% of sites rise in combinations of Staurosira construens and varieties, respectively. More comprehensive is the impact of increased Staurosirella pinnata and Pseudostaurosirella brevistriata. These taxa sediment flux with evidence for increased sedimentation rate, are considered to prefer disturbed, low light environments with turbidity or macrophyte loss in 80% of sites analysed. In concert reduced substrate diversity and so attest to increased turbidity and they reveal the comprehensive nature of the changes that have loss of macrophytes (Gell et al., 2002; Hay et al., 2000). The range of 42[(Fig._1)TD$IG] P. Gell, M. Reid / Anthropocene 8 (2014) 39–45

Fig. 1. Location of sediment records examined across the southern Murray Darling Basin. Numbers refer to those in Table 1. sites that support these flora include the Coorong coastal estuary the condition of rivers against expected, natural conditions (Davies and the terminal Lake Alexandrina (Fluin et al., 2007), floodplain et al., 2012). The Ramsar Convention on the protection of wetlands lakes such as Sinclair Flat in (Grundell et al., 2013), of international significance attempts to identify ‘natural ecologi- Lake Cullulleraine (Fluin et al., 2010) and Kings Billabong (Kattel cal character’ which is often that described at the time a wetland is et al., in press) near Mildura and as far upstream as Coonoocoocabil added to the register of sites, and the Water Framework Directive Lagoon A on the Murrumbidgee River near Gundagai (Gell and aims to return European waterways to ‘good ecological condition’ Little, 2006). In most upper systems this change to plankton is (Bennion and Battarbee, 2007). Where human impacts have a long evident in rises in the river plankton Aulacoseira spp. This is history, and are multi-faceted, contemporary measures, and even particularly so in the large, deep sites near Albury (Reid et al., 2007) recent comparisons, prove futile in assessing the condition of a where plankton has replaced epiphytic flora, but also in the lower wetland before impacted by industrialised humanity. Further, catchment such as at Sinclairs Flat. Evidence for wetland particularly where climates are variable, benchmarks ought to salinisation is also concentrated in the lower catchment with report on historic range of variability, and so need to characterise widespread increases in Amphora coffeaeformis, Gyrosigma spp., the response of systems to variations in non-human drivers to gain Nitzschia frustulum, Pleurosigma spp. and Tryblionella spp., but it is insight into internal dynamics. Given the low frequency of high also evident at Coonoocoocabil Lagoon B on the Murrumbidgee impact climate cycles it could be argued that benchmarks require River. Evidence for the increase in river salinity may be drawn from temporal context spanning millennia. the widespread emergence of Actinocyclus normannii in recent The record represented in the sediments of few floodplain sites sections of floodplains wetlands, however this species may also be span this time frame. Tareena Billabong commenced accumulating reflecting widespread nutrient enrichment. Enrichment is sediment 5000 years ago and it was revealed to be a freshwater reflected in recent rises in Stephanodiscus hantzschii and Gompho- lagoon at the time (Gell et al., 2005a). It underwent relatively little nema spp. in upstream, freshwater sites, and Cyclotella meneghini- variation in response to Holocene climate variability after a brief ana more broadly, but including sites where salinity levels are phase of increased river connectivity ending 3000 years ago. Even higher such as at Psyche Bend Lagoon near Mildura. The so, this record attests to the fact that a range of ‘natural’ conditions widespread decline in Epithemia spp., diatoms known to be can be invoked depending upon which point in time is chosen. competitive in low nutrient waters by virtue of their nitrogen- Muroondi wetland, towards the terminus of the river channel, fixing endosymbionts (Stancheva et al., 2013), may also attest to holds a surprisingly deep 14 m of sediment. The record here increased ambient nitrate levels across the system. Lastly, reveals a 5000 year record of hydroseral evolution with planktonic acidification is known from three sites examined here and, while forms increasingly replaced by those of shallow waters and only Martins Bend shows increases in acidophilous taxa such as eventually epiphytic diatoms reflecting the evolution of a Pinnularia spp. (Gell, 2010), Loveday Swamp and Psyche Bend marshland in a shallow basin. This site attests to directional Lagoon both showed increases in the sulphur preferring taxon change which occurs as sediments naturally infill (Gell et al., Haslea spicula before drying lead to oxidation which, in turn, 2005b). triggered acidification. Human impact Natural ecological character The impact of indigenous people on Murray River floodplains Many natural resource management instruments attempt to wetlands is not well revealed in the sediment records. While direct identify a benchmark condition against which to assess contem- burning of wetland vegetation is invoked from charcoal records of porary condition. In Australia the Sustainable Rivers Audit assessed sites elsewhere (Head, 1988; Mooney et al., 2011; Mills et al., P. Gell, M. Reid / Anthropocene 8 (2014) 39–45 43

2013), the routine analysis of charcoal from floodplain wetlands wetland condition. Only the palaeoecological record has been able remains an important area of future endeavour. In the absence of to reveal the consequences of the weakening, or strengthening, of charcoal records, inference for the impact of early humans on certain feedbacks, and more detailed analysis of the nature of these wetlands is left to ethnohistoric and archaeological evidence. abrupt shifts promises much in our understanding of threshold The sediment records do, however, strongly attest to the changes. The widespread and, at times, coincident nature of the substantial and widespread impact of humans since settlement by changes observed suggest the cause for wetland decline is less Europeans. The most significant change attributable to a post- likely site-by-site regimes shifts, but is due to basin-wide decline contact age is a sustained increased in diatom-inferred salinity, in the condition of the river waters themselves. Further exploration from 1880 AD, at Tareena Billabong as indicated by substantial of the hydrological controls of wetland function, such as degree of increases in the abundance of Amphora veneta, Gyrosigma connectivity, will strengthen interpretations of the similarities, apiculatum and Tryblionella hungarica. This early impact is and differences, in the changes recorded from this broad suite of attributable to intense use of the site lying alongside a narrow sites. passage for stock to be run between the distributory system and the dunefields. Elsewhere, salinisation, reflected by sustained Management implications increases in salt tolerant diatoms, is widely evident. Psyche Bend Lagoon naturally supported oligosaline taxa but became hypersa- This synthesis has greatly strengthened knowledge of the line by the early 21st century. Diatom-based salinity reconstruc- degraded nature of the wetlands of the Murray Darling Basin by tion shows that sites deemed to be in good condition, such as Loch providing a comprehensive assessment of change relative to a Luna, have undergone ten-fold increases in salinity (Gell et al., long-term, and at times, pre-European settlement baseline of 2007). A wide range of usually cosmopolitan diatom species are ecological condition. It has also expanded the spatial extent of the indicative of elevated nutrient concentrations (Chessman et al., previously reported palaeolimnological changes (Gell et al., 2009) 2007). The increase, in sediment records across the basin, in these across the basin. While these records are skewed towards the more taxa reveal the chronic eutrophication of the system. Further, a permanent wetlands in the basin that continuously accumulate suite of tychoplanktonic species (Pseudostaurosira spp., Staurosir- sediments, the wetlands represent unrivalled, continuous recor- ella spp; Staurosira spp.), that appear to be advantaged by high ders of change over time and they attest to the universal turbidity in Australian shallow lakes, have come to dominate, degradation of the condition of the waterways of the southern sometimes abruptly, in a wide range of sites (Fluin et al., 2007, Murray Darling Basin. They verify that nutrients and salts have 2010; Grundell et al., 2013) reflecting widespread impact in the impacted many wetlands and that sediment flux to wetlands is a form of excessive fine sediment inputs. This is also reflected in major threat to their condition. The long term perspective reveals substantial and widespread increases in sedimentation rates from that impacts occurred from early in European settlement and that a baseline of 0.1–1 mm/a to 10–40 mm/a (Gell et al., 2009). While any estimate of condition change based on a reference sites is liable both the extensive clearance of vegetation and stock grazing (Reid to greatly underestimate the magnitude of change. While wetland et al., 2007), as well as stream bank collapse (Olley and Wallbrink, drying remains an ongoing risk this evidence also questions the 2004), have been implicated, the precise pathway of fine sediments prospects of recovery after the implementation of costly environ- to these wetlands remains unclear. Such high rates of accretion, in mental flow allocations in the absence of complementary such shallow wetlands, poses a great risk to the persistence of measures to alleviate the impacts of nutrient, salt and sediment these depressions as wetland sites and represents a significant risk flux, particularly as the river channels are a likely source of these to the Basin’s ecosystems (Laurance et al., 2011). Lastly, exposure pollutants. Contemporary monitoring is the mainstay of ecosystem of sulphidic sediments, through low water levels during the condition assessment but, given the low frequency cycles at play Millennium drought, has driven unprecedented acidification (Gell, with human impact, the magnitude of the risk to ecosystems 2010). The colonisation of the diatom Haslea spicula in two of these services and the management challenge is only understood when sites, before acidification, may mark this species as an early complemented with evidence of change over the longer term. warning indicator of this risk. Despite comprehensive assessment of the condition of the waterways of the Murray Darling Basin, the impact of agricultural Regime shifts development, and the risk to ecosystem services, is often under- estimated. Investigations into the intensification of agriculture in Wetlands are known to undergo abrupt changes in condition on northern Australia to serve economic development goals have account of the breakdown of stabilising forces that tend to direct drawn warnings from observations of the impact such intensive the condition of wetlands to a stable state, enabling a greater development has wrought on the Murray Darling Basin (Davis variation in condition that may approach thresholds of ‘irrevers- et al., submitted for publication). These lessons are strengthened ible’ change (Scheffer et al., 1993). One such threshold relates to by the evidence for the sensitivity of Australian systems to the light regime whereby aquatic plants, attached to substrates, development that come from records that provide evidence for the receive less energy as turbidity impacts upon the light regime and changes that commenced in the early days of settlement. These their capacity to photosynthesise. Abrupt changes to Murray extended histories call for caution in the northward expansion of Darling wetlands have been observed, sometimes delayed relative intensive agriculture. to the onset of likely drivers, suggesting a non-linear, threshold response may be at play. The most vulnerable of the Murray River Conclusion floodplain wetlands are those which are large and deep where high proportions of the benthic habitat of the wetland become energy Palaeolimnological approaches shine a light on the nature and limited once increased turbidity reduces the penetration of light magnitude of human impact on the floodplain wetlands of the (Reid et al., 2007). More shallow sites in the upper catchment are Murray Darling Basin. Many wetlands have been substantially thought to be resilient to reduced light penetration and those in the changed on account of river regulation, abstraction, eutrophica- lowlands able to reset after drying (Reid and Gell, 2011). Detailed tion, salinisation, acidification and declining light regime. Some analysis is essential to understand the light and trophic dynamics changes occurred early in European settlement and, in many cases, that may be controlling the changes recorded from the sediments changes were abrupt. The report card for the condition of the to enable managers to most effectively intervene to recover wetlands of the Murray Darling Basin, at least those studied 44 P. Gell, M. Reid / Anthropocene 8 (2014) 39–45 palaeolimnologically to date, is one of severe, widespread Gell, P., Baldwin, D., Little, F., Tibby, J., Hancock, G., 2007. The impact of regulation and salinisation on floodplain lakes: the lower River Murray, Australia. Hydro- degradation. Sediment fluxes, in particular, risk the very existence biologia 591, 135–146. of many wetland sites. The poor quality of the water of the rivers Gell, P., Barker, P., De Deckker, P., Last, W., Jelicic, L., 1994. The Holocene history of themselves suggests that the mere provision of water will not West Basin Lake, Victoria, Australia; chemical changes based on fossil biota and sediment mineralogy. J. Paleolimnol. 12, 235–258. reinstate benchmark conditions. Moreover, the likelihood of non- Gell, P., Bulpin, S., Wallbrink, P., Bickford, S., Hancock, G., 2005a. Tareena Billabong – linear responses in the early post-settlement makes successful a palaeolimnological history of an everchanging wetland, Chowilla Floodplain, restoration or rehabilitation even more challenging. Research to lower Murray-Darling Basin. Mar. Freshw. Res. 56, 441–456. date has focussed on the southern basin and understanding of the Gell, P., Fluin, J., Tibby, J., Hancock, G., Harrison, J., Zawadzki, A., Haynes, D., Khanum, S., Little, F., Walsh, B., 2009. Anthropogenic acceleration of sediment accretion Basin as a whole would benefit from the extension of these in lowland floodplain wetlands, Murray-Darling Basin, Australia. Geomorphol- approaches to other regions. ogy 108, 122–126. Gell, P., Fluin, J., Tibby, J., Haynes, D., Khanum, S., Walsh, B., Hancock, G., Harrison, J., Zawadzki, A., Little, F., 2006. Changing fluxes of sediments and salts as recorded Acknowledgments in lower River Murray wetlands, Australia. In: Rowan, J., Duck, R., Werrity, A. (Eds.), Proceedings of the IAHS conference, Dundee, UK, July 2006, vol. 306. International Association of Hydrological Sciences, pp. 416–424. This synthesis relies on the records of change produced by Gell, P., Little, F., 2006. Water Quality History of Murrumbidgee River Floodplain many colleagues and students. The work of Kate Adamson, David Wetlands. Murrumbidgee Catchment Management Authority, Wagga Wagga. Baldwin, Jennie Fluin, Rosie Grundell, Garry Heinitz, Ifteara Gell, P.A., Sluiter, I.R., Fluin, J., 2002. Seasonal and inter-annual variations in diatom Khanum, Fiona Little, Sorell Lock, Ralph Ogden, Martin Thoms, assemblages in Murray River-connected wetlands in northwest Victoria, Australia. Mar. Freshw. Res. 53, 981–992. John Tibby and Brendan Walsh is greatly appreciated. The original Gell, P., Tibby, J., Fluin, J., Leahy, P., Reid, M., Adamson, K., Bulpin, S., MacGregor, A., studies were supported by Australian Research Council Linkage Wallbrink, P., Hancock, G., Walsh, B., 2005b. Accessing limnological change and grants (LP0560552 and LP0667819) to PG and several grants variability using fossil diatom assemblages, south-east Australia. Riv. Res. Appl. 21, 257–269. through the Australian Institute for Nuclear Science and Gergis, J., Gallant, A.J.E., Braganza, K., Karoly, D.J., Allen, K., Cullen, L., D’Arrigo, R., Engineering. Further support was provided by the Murrumbidgee Goodwin, I., Grierson, P., McGregor, S., 2012. On the long-term context of the Catchment Management Authority, the River Murray Catchment 1997–2009 ‘Big Dry’ in south-eastern Australia: insights from a 206-year multi- proxy rainfall reconstruction. Clim. Chang. 111 (3), 923–944. Water Management Board and the South Australian Department of Giorgi, F., 2006. Climate change hotspots. Geophys. Res. Lett. 33, L08707, http:// Water, Land and Biodiversity Conservation. Support for PG to dx.doi.org/10.1029/2006GL025734. attend the PAGES Human-Climate-Ecosystem Interactions work- Grundell, R., Gell, P., Zawadzki, A., Mills, K., 2013. Interaction between a river and its wetland: evidence from spatial variability in diatom and radioisotope records. shop meeting in Leuven to present this paper was provided by the J. Paleolimn. 47, 205–219. Collaborative Research Network of Federation University Australia. Hay, M.B., Michelutti, N., Smol, J.P., 2000. Ecological patterns of diatom assemblages The authors appreciate the comments from two anonymous from MacKenzie delta lakes, Northwest Territories, Canada. Can. J. Bot. 78, 19–33. reviewers. Head, L., 1988. Environment as artefact. Aust. J. Ecol. 13, 21–49. Kattel, G., Gell, P., Perga, M., Jeppesen, E., Grundell, R., Weller, S., Zawadzki, A., Barry, L., in press. Tracking a century of change in trophic structure and dynamics in a References floodplain wetland: integrating palaeo-ecological, and palaeo-isotopic, evi- dence. Freshw. Biol., http://dx.doi.org/10.1111/fw.12521 (in press). Laurance, W.F., Dell, B., Turton, S.M., Lawes, M.J., Hutley, L.B., McCallum, H., Dale, Adamson, K., 2002. A palaeoecological investigation of late Holocene environment P.,Bird,M.,Hardy,G.,Prideaux,G.,Gawne,B.,McMahon,C.R.,Yu,R.,Hero,J.- variability and the impact of European settlement in the lower Murray Basin. M.,Schwarzkopf,L.,Krockenberger,A.,Douglas,M.,Silvester,E.,Mahony,M., Geography and Environmental Science, Monash University. Vella, K., Saikia, U., Wahren, C.-H., Xu, Z., Smith, B., Cocklin, C., 2011. The Bennion, H., Battarbee, R.W., 2007. The European Union Water Framework Direc- 10 Australian ecosystems most vulnerable to tipping points. Biol. Cons. 144, tive: opportunities for paleolimnology. J. Paleolimn. 38, 285–295. 1472–1480. Bowler, J.M., Johnston, H., Olley, J.M., Prescott, J.R., Roberts, R.G., Shawcross, W., McMahon, T.A., Finlayson, B.L., 1992. Global Runoff: Continental Comparisons of Spooner, N.A., 2003. New ages for human occupation and climatic change at Annual Flows and Peak Discharges. Catena, , pp. 166 pp. Lake Mungo, Australia. Nature 421 (6925), 837–840. Mills, K., Gell, P., Gergis, J., Baker, P., Finlayson, M., Hesse, P., Jones, R., Kershaw, P., Chessman, B., Bate, N., Gell, P.A., Newall, P., 2007. A diatom species index for Pearson, S., Treble, P., Barr, C., Brookhouse, M., Drysdale, R., McDonald, J., bioassessment of Australian rivers. Mar. Freshw. Res. 58 (6), 542–557. Haberle, S., Reid, M., Thoms, M., Tibby, J., 2013. Paleoclimate studies and Davies, P.E., Stewardson, M.J., Hillman, T.J., Roberts, J.R., Thoms, M.C., 2012. Sus- natural-resource management in the Murray-Darling Basin II. Unravelling tainable Rivers Audit 2: the ecological health of rivers in the Murray–Darling human impacts and climate variability. Aust. J. Earth Sci. 60, 561–571. Basin at the end of the Millennium Drought (2008–2010). Summary. Murray Mooney, S.D., Harrison, S.P., Bartlein, P.J., Daniau, P.J., Stevenson, A.-L., Brownlie, J., Darling Basin Authority, Canberra. Buckman, K.C., Cupper, S., Luly, M., Black, J., Colhoun, M., D’Costa, E., Dodson, Davis, J.A., O’Grady, A.P., Dale, A., Arthington, A.H., Gell, P., Driver, P., Bond, N., D.,Haberle,J.,Hope,S.,Kershaw,G.S.,Kenyon,P.,McKenzie,C.,Williams,M.N., Casanova, M., Finlayson, M., Watts, R., Capon, S., Nagelkerken, I., Tingley, R., Fry, 2011. Late Quaternary fire regimes of Australasia. Q. Sci. Rev. 30 (1–2), B., Page, T.J., Specht, A., submitted for publication. When trends collide: the 28–46. challenge of protecting freshwater ecosystems under multiple land use and Norris, R.H., Liston, P., Davies, N., Coysh, J., Dyer, F., Linke, S., Prosser, I., Young, B., hydrological intensification scenarios. Sci. Total Environ. (submitted for publi- 2002. Snapshot of the Murray-Darling Basin River Condition. Cooperative cation). Research Centre for Freshwater Ecology, Canberra. Fluin, J., Gell, P., in preparation. Sediment-derived scenarios of wetland status and Ogden, R.W., 2000. Modern and historical variation in aquatic macrophyte cover of change, the Lower River Murray, SA. Report for the River Murray Natural billabongs associated with catchment development. Regul. Rivers: Res. Manage. Resource Management Board (in preparation). 16, 497–512. Fluin, J., Gell, P., Haynes, D., Tibby, J., 2007. Paleolimnological evidence for the Olley, J., Wallbrink, P., 2004. Recent trends in turbidity and suspended sediment independent evolution of neighbouring terminal lakes, the Murray Darling loads in the Murrumbidgee River, NSW, Australia. Int. Assoc. Hydrol. Sci. 288, Basin, Australia. Hydrobiologia 591, 117–134. 125–129. Fluin, J., Tibby, J., Gell, P., 2010. Testing the efficacy of electrical conductivity (EC) Pardoe, C., 1998. The cemetery as symbol: the distribution of pre-historical Aborig- reconstructions from the lower Murray River (SE Australia): a comparison inal burial grounds in southeastern Australia. In: Murray, T. (Ed.), Archaeology between measured and inferred EC. J. Paleolimn. 43, 309–322. of Aboriginal Australia: A Reader. Allen and Unwin, Sydney. Gell, P.A., 1997. The development of a diatom data base for inferring lake salinity: Philibert, A., Gell, P., Newall, P., Chessman, B., Bate, N., 2006. Development of towards a quantitative approach for reconstructing past climates. Aust. J. Bot. diatom-based tools for assessing stream water quality in south eastern 45, 389–423. Australia: assessment of environmental transfer functions. Hydrobiologia Gell, P., 2010. With the Benefit of Hindsight: the utility of palaeoecology in wetland 572, 103–114. condition assessment and identification of restoration targets. In: Batty, L., Reid, M.A., 2002. A diatom-based palaeoecological study of two billabongs on the Hallberg, K. (Eds.), Ecology of Industrial Pollution. Ecological Review Series, CUP Goulburn River floodplain, southeast Australia. In: John, J. (Ed.), Proceedings of & British Ecological Society, New York, pp. 162–188. the15th International Diatom Symposium. Gantner Verlag, Ruggell, pp. 237– Gell, P.A., 2012. Palaeoecology as a means of auditing wetland condition. In: 253. Haberle, S.G., David, B. (Eds.), Peopled Landscapes: Archaeological and Biogeo- Reid, M.A., 2008. Evidence for catastrophic shifts in the trophic structure of graphic Approaches to Landscapes, 34. Terra Australis, pp. 445–457. floodplain lakes associated with soil erosion. In: Schmidt, J., Cochrane, T., Gell, P., in press. The Coorong. In: Weckstrom, K., Gell, P., Saunders, K., Skilbeck, G. Phillips, C., Elliot, S., Davies, T., Basher, L. (Eds.), Sediment Dynamics in Changing (Eds.), The Palaeolimnology of Estuarine Systems, Developments in Paleoenvir- Environments. IAHS Press, Wallingford, UK, pp. 584–590. onmental Research. Kluwer, Dordrecht. P. Gell, M. Reid / Anthropocene 8 (2014) 39–45 45

Reid, M.A., Fluin, J., Ogden, R., Tibby, J., Kershaw, P., 2002. Long-term perspectives on Thoms, M.C., Ogden, R.W., Reid, M.A., 1999. Establishing the condition of lowland human impacts on floodplain-river ecosystems, Murray-Darling Basin, floodplain rivers: a palaeo-ecological approach. Freshw. Biol. 41, 407–423. Australia. Verh. Internat. Verein Limnol. 28, 710–716. Tibby, J., Reid, M.A., 2004. A model for inferring past conductivity in low salinity Reid, M., Gell, P., 2011. Regional wetland response typology, Murray-Darling Basin, waters derived from Murray River diatom plankton. Mar. Freshw. Res. 55, Australia. PAGES News 19, 62–64. 587–607. Reid, M.A., Sayer, C.D., Kershaw, A.P., Heijnis, H., 2007. Palaeolimnological evidence Van Dam, H., Mertens, A., Sinkeldam, J., 1994. A coded checklist and ecological for submerged plant loss in a floodplain lake associated with accelerated indicator values of freshwater diatoms from the Netherlands. Neth. J. Aquat. catchment soil erosion (Murray River, Australia). J. Paleolimn. 38, 191–208. Ecol. 28 (1), 117–133. Scheffer, M., Hosper, S.H., Meijer, M.L., Moss, B., 1993. Alternative equilibria in Warner, R.F., 1987. The impacts of alternating flood- and drought-dominated shallow lakes. Trends Ecol. Evol. 8, 275–279. regimes on channel morphology at Penrith, , Australia. Int. Stancheva, R., Sheath, R.G., Read, B.A., McArthur, K.D., Schroepfer, C., Kociolek, J.P., Assoc. Hydrol. Sci. 68, 327–338. Fetscher, A.E., 2013. Nitrogen-fixing cyanobacteria (free-living and diatom Wittwer, D., Dixon, J., 2013. Effective use of public funding in the Murray-Darling endosymbionts): their use in southern California stream bioassessment. Hydro- Basin: a comparison of buy-backs and infrastructure upgrades. Aust. J. Agric. biologia 720, 111–127. Res. Econ. 57, 399–421.