Impact of excess freshwater flow on the lower barratta creek and estuary



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IMPACT OF EXCESS FRESHWATER FLOW ON THE

LOWER BARRATTAS CREEK AND ESTUARY

Report No. 12/09
November 2012
Working Draft No. 12/08

September 2012


IMPACT OF EXCESS FRESHWATER FLOW ON THE

LOWER BARRATTA CREEK AND ESTUARY


Report No. 12/09

November 2012

Prepared by Damien Burrows, Marcus Sheaves, Ross Johnston, John Dowe and Jason Schaffer

TropWATER - Centre for Tropical Water and Aquatic Ecosystem Research

James Cook University,

Townsville, Qld. 4811

Phone: (07) 47814262

Fax: (07) 47815589

email: actfr@jcu.edu.au

website: www.actfr.jcu.edu.au



4. DISCUSSION 39

5. CONCLUSIONS 42

General Site Photos – Floating Aquatic Weeds Impacting East Barratta Creek, Downstream of the Bruce Highway 48

Salvinia-infested reach Hyacinth-infested reach General Site Photos – Aquatic Weeds Impacting Wetlands on East Barratta Creek Floodplain 49

49


General Site Photos – West Barratta Creek Floodplain 50

General Site Photos – Mangrove Inundation – Freshwater/Estuarine Interface, East Barratta Creek 51

General Site Photos – Mangrove Dieback – Freshwater/Estuarine Interface, East Barratta Creek 52


EXECUTIVE SUMMARY
Barratta Creek is arguably the most important floodplain habitat within the Burdekin-Dry Tropics region. It retains reasonable riparian vegetation condition, has few physical fish passage barriers (none along the main creek channel) and retains reasonable water quality and fish community health. Despite having high values, the wetlands of Barratta Creek have generally not been actively managed and their condition is threatened by a range of management issues. Barratta Creek has only been subject to intensive development relatively recently, since the irrigation scheme came on line in the 1990’s and the declining condition of its aquatic and riparian habitats can be readily witnessed as occurring presently. Recently, it has been observed that mangroves are dying at the freshwater-estuarine interface and that the exotic aquatic weed hymenachne has spread significantly across the lower Barratta floodplain. Local residents observed that the build-up of dense hymenachne stands was changing the flow direction of water, causing erosion as water cut new channels and increasing flooding on the access road to the fishing community of Jerona. In addition to this significant increase in hymenachne, there has been a build-up of surface floating weeds such as water hyacinth in the freshwater reaches of the lower creek system, covering much of the water surface and mangrove dieback is occurring at the freshwater-estuarine interface. TropWATER was commissioned by NQ Dry Tropics NRM to undertake an assessment of the extent, impact and possible causes of these weed invasions, mangrove dieback, and changes to water quality and faunal assemblages, in both the freshwater and upper estuarine ecosystems of Barratta Creek.
This study found that large lengths of lower Barratta Creek, especially the east branch, are heavily infested by floating aquatic weeds – mainly water hyacinth, but also salvinia and water lettuce. These dense mats have created conditions of very poor water quality, especially for dissolved oxygen, and this has resulted in depauperate fish species richness compared to what is found in reaches further upstream. The amount of aquatic habitat negatively affected in this way is extensive and significant. Fortunately, it appears that estuarine-breeding fish such as barramundi are present above the weed choke, suggesting that fish passage through these weed-choked reaches is still viable for the time being.
The distribution of the exotic weed, hymenachne was found to be extensive and significantly impacting on the habitat values of nearly all wetlands on the Barratta floodplain, including across the saltpans, which are now evidently fresh enough to support their presence. The largest infestations are associated with ponded areas, either natural or constructed, or where stream width increases and water depths diminish. The mangrove dieback at the freshwater-estuarine interface on East Barratta Creek is not extensive but most likely directly related to the excess freshwater coming down the creek, effectively drowning the trees roots, through prolonged inundation. At the estuarine interface, hymenachne and a number of native submerged macrophytes are growing on former saltpans and underneath mangrove trees, a situation created by the excess freshwater flow during the dry season. Fortunately, although the excess freshwater has altered the salinity regime of the East Barratta Creek estuary, no significant impacts upon the fauna there were observed.
Although there are multiple drivers of the deteriorating condition of the lower Barratta Creek system, all of the impacts recorded in this study can be traced to the excess freshwater flow during the dry season, when the creek would normally cease to flow. This excess flow, all of it irrigation water, is causing mangrove dieback and altering the nature of the freshwater-estuarine interface. The perennial freshwater flow also creates ideal growing conditions for exotic weeds, which would be more readily controlled if a more natural seasonal flow regime was present.
Although aquatic weed management was also a major focus of the 2007 Barratta Creek management plan, the extent of weed infestation in the lower reaches has not until now, been recognised as being as significant as it is. The significant extent of these weed problems are not well-recognized and need to be brought to the attention of relevant authorities.

1. INTRODUCTION
Barratta Creek is arguably the most important floodplain habitat within the Burdekin-Dry Tropics region. Compared to other developed coastal catchments of Queensland’s tropical coast, including the rest of the Burdekin-Haughton floodplain, the remnant wetlands of the Barratta Creek catchment have exceptionally high ecological and functional values which have been recognised by listings in the National Directory of Important Wetlands in Australia and the estuarine/coastal wetlands are within the Ramsar-listed Bowling Green Bay wetland aggregation. Riparian vegetation is relatively intact compared to most watercourses in the region and provides migratory paths for both terrestrial and aquatic fauna throughout the catchment. Additionally, there are no major physical fish passage barriers such as weirs, to impede fish migration and connectivity, again, something of a rarity in the Burdekin catchment and along the developed coast of Queensland. Despite having high values, these wetlands have generally not been actively managed and their condition is threatened by a range of management issues.
Barratta Creek has been the subject of previous investigations on habitat values and water quality. Scientific and environmental assessment work done in aquatic habitats of the catchment up to 2007 was summarised in Veitch et al. (2007). Though in better condition than many other catchments, Barratta Creek has only been subject to intensive development relatively recently, since the irrigation scheme came on line in 1994 and the declining condition of its aquatic and riparian habitats can be readily witnessed as occurring presently (Burrows and Butler 2007). Some of these impacts arise as new issues, not previously encountered. Tait and Veitch (2007) prepared a management plan for the catchment which dealt with the main threats as known at that time. The alteration of the flow regime, with excess freshwater flowing down the system throughout the year, was one of the key management issues identified.
Recently, it has been observed that mangroves are dying at the freshwater-estuarine interface and that the exotic aquatic weed hymenachne has spread significantly across the lower Barratta floodplain. Local residents observed that the build-up of dense hymenachne stands was changing the flow direction of water, causing erosion as water cut new channels and increasing flooding on the access road to the fishing community of Jerona. In addition to this significant increase in hymenachne, there has been a build-up of surface floating weeds such as water hyacinth in the freshwater reaches of the lower creek system, covering much of the water surface. The presence and deleterious impact of these aquatic weeds was recognised by Tait and Veitch (2007) but their extent has increased greatly since that document was prepared.
Barratta Creek is used to deliver irrigation water to cane farms along its length. Additionally, tailwater from these (mostly flood-irrigated) farms, also enters the creek. Thus, the creek flows perennially, when naturally it only had seasonal flow. The greatly elevated dry season flow is increasing water volumes reaching the lower freshwater and upper estuarine reaches. This is contributing to the development of large infestations of aquatic weeds in the lower freshwater reaches and believed to be causing mangrove dieback in the upper estuarine reaches.
TropWATER – the Centre for Tropical Water and Aquatic Ecosystem Research at James Cook University in Townsville, was commissioned by NQ Dry Tropics NRM to undertake an assessment of the extent, impact and possible causes of these weed invasions, mangrove dieback, and changes to water quality and faunal assemblages, in both the freshwater and upper estuarine ecosystems of Barratta Creek.



    1. Hymenachne: Hymenachne amplexicaulis

Hymenachne (Hymenachne amplexicaulis) is an invasive grass that is estimated to cover about 14,000 hectares in Queensland, Northern Territory and northern New South Wales (WONS 2011). It is a perennial semi-aquatic grass that has invaded high value conservation wetlands, blocks waterways and infests low lying crops. It ultimately impedes water flow and significantly alters habitat composition and structure. The grass was introduced to Australia as a ponded pasture fodder crop in the late 1980s. The species is native to South America, and the invasive form is the cultivar ‘Olive’ (Sharp and Simon 2002), hence the common name olive hymenachne.


Hymenachne is a robust, stoloniferous and matt-forming grass, with branching stems 2–3.5 m tall. The stems root strongly from the nodes. The leaf blades, which are up to 40 cm long to 6 cm wide, have a distinctive base that encircles the stem. The inflorescence, 10-38 cm long by 1–1.5 cm wide, is a tight panicle that looks somewhat cylindrical as the individual branches are held almost parallel to each other (Cowie et al. 2000).
Hymenachne is readily spread by either seeds or vegetatively. Small stem portions are able to re-establish as long as an intact node is present. Stem portions are mainly spread by flowing water and the movement of animals. Seeds, which are prolifically produced, are dispersed by water, birds or on the fur or hooves of animals. Germination rates are very high when seeds are deposited in wet areas, but rates are much less reduced in drier locations. Buried seeds can remain viable for up to four years (DNRMW 2006).
Early detection and the prevention of spread are integral to its control. Management and eradication of hymenachne are best achieved by mechanical removal, especially from areas where it has recently invaded and yet to become established (DNRMW 2006). Optimum environmental conditions include slow flowing water, in areas where little or no shade is present.
The Barratta Creek system is a high value vegetation corridor but is afflicted by a growing weed problem. Much of the creek system within the irrigated sugar cane lands is deeply incised and covered by a well-developed riparian canopy. Hymenachne infestations are inclined not to develop in these environments because of over-shading and dynamic floods. However, in the downstream sections, stream definition becomes less pronounced and divides into multiple channels and broad water bodies, environments in which hymenachne will develop large and dense populations. The downstream areas are primarily used for cattle grazing. Distinct channels appear again within the mangrove region. In the mangrove sections, hymenachne is more or less absent from the main channels because of saline influence, but is prevalent on adjacent banks and slopes where freshwater levels are increased. ACTFR have previously conducted a limnology survey along upstream sections of East Barratta Creek by boat in March 2005 (Burrows and Davis 2005) and on foot (Dowe 2009), recording the presence of hymenachne along the way.

1.2 Connectivity in a Developed Floodplain
The Burdekin delta is an area in which freshwater–marine connectivity has been highly impacted as a result of agricultural practices. The Burdekin irrigation scheme provides year-round water to sugar cane producers, with water sourced from the Burdekin Falls Dam, delivered to farms then dispersed through distributary streams to the coast.
Rainfall, and consequent freshwater flows are highly seasonal in the dry tropics with wet summers and dry winter/springs so fresh-marine connectivities might be expected to mirror that seasonal pattern with good connectivity during the wet season and poor or no connectivity during the dry. Inputs of freshwater from irrigation might be expected to enhance dry season fresh-marine connectivity across the delta but because much of the agricultural land in the delta is marginal there have been substantial anthropogenic modifications to water flows to enhance agricultural potential. At present there are more than 1500 bund walls in place to prevent ingress of salt water onto marginal agricultural land and/or to create freshwater impoundments (Alluvium 2007) and each of these acts as a barrier to freshwater-marine connectivity. Barratta Creek and its associated wetland is the only stream system in the delta that has not had a bund wall constructed to reduce interchange between fresh and tidal waters.
Despite its location in the dry tropics, salinity profiles in Barratta Creek resemble those of a wet tropics stream with depressed upstream salinities (13 – 17 ppt) during the dry season when downstream salinities ranged from were close to or above 35 ppt (Sheaves & Johnston 2009). In a dry tropics estuary the expectation would be salinities approaching or above marine salinities (35 ppt) in upstream reaches (Robertson et al. 1988, Ridd and Stieglitz 2002) rather than depressed salinities such as those reported by Sheaves and Johnston (2009). This data provided a clear indication that freshwater inputs do not cease during the dry season in Barratta Creek and this suggests considerable dry season inflows of irrigation water.
Being the only system in the delta with no bund walls and potentially good year-round fresh-marine connectivity makes Barratta Creek an important system for the maintenance/retention of diversity of biological processes in the region. However, in recent years the condition of wetlands near the upper limits of tidal incursion has deteriorated markedly as a result of infestations of noxious aquatic weeds. Recent accumulations of weed biomass have choked the main creek channel effectively stifling connectivity through the wetlands in much the same way as a bund wall would.
The weed choke has lead to greater retention of freshwater upstream from the choke and the cessation of tidal ingress, two factors that appear to have contributed to loss of mangroves around creek fringes upstream from the choke. In addition, the bunding effect of the choke has caused divergence in water flow across parts of the wetland leading to apparent discharge into an adjacent estuary system, Barramundi Creek. Prior to the weed choke in Barratta Creek it was likely that Barramundi Creek only received water from the Barratta wetland during flood events.
As part of their noxious weed eradication program the natural resource management body for north Queensland’s dry tropics commenced removal of the weed choke in Barratta Creek late in 2011 with the express intention of re-establishing the freshwater-marine connectivity for the system. Removal of the choke would return most of the irrigation water to Barratta Creek and greatly reduce freshwater flows through the wetland to Barramundi Creek. Removal of the choke should, in theory at least, initiate changes to the upstream salinity regimes of the two systems with potential to remove dry season freshwater flows to Barramundi Creek and increase freshwater flow volumes to Barratta Creek.
In addition to potential shifts in salinity regime in the upper reaches of both estuary systems resulting from removal of the weed choke there is also a potential response from faunal assemblages due to those salinity shifts (Blaber et al., 1989, Sheaves 1998). Anecdotal reports from local landholders and fishermen suggested they have experienced large declines in fish and mud crab catches from Barratta Creek and that the system was in a very poor state at present. Although these indications can not necessarily be related directly to the weed choke and stifling of connectivity, they do raise broader questions about fish and crab assemblages and what pressures they may be under.

2. METHODS


This work is focused around assessing the extent of aquatic weeds and the impact they are having on water quality and faunal communities. It is readily obvious that there is a large amount of freshwater flowing into the upper estuarine reaches of Barratta Creek, including during the dry season when such flows would, under natural conditions, have ceased. It is also obvious that there are extensive areas of various aquatic weeds in the lower freshwater reaches.
This work was focused around three major areas of work:

  1. Riparian and mangrove vegetation condition and the invasion of hymenachne across the floodplain

  2. Impact of aquatic weeds on water quality and fish communities in lower freshwater reaches

  3. Impact of excess freshwater flow on water quality and faunal communities in upper estuarine habitats


2.1 Riparian Vegetation and Hymenachne Distribution
The distribution hymenachne along the East and West Barratta Creeks downstream of the Bruce Highway crossing were undertaken during 28-29 May, and 13-14 August, 2012. In addition, we examined the possible causes of decline/death of mangrove trees in the downstream sections. The sites were visited on foot, and each site was photographed and GPS co-ordinates recorded. Notes on infestation intensity, environmental variables, dominant vegetation, and other weeds were taken.

2.2 Habitat Condition in Freshwater Reaches
2.2.1 Water Quality
Water quality was assessed by deployment of Hydrolab Datasonde’s (DS) at four sites, one upstream of the weed choke and three within the weed choked sections. These were deployed from a boat and attached by cable ties to a large star picket driven into the substrate and a float for bouyancy. Unfortunately, the Hydrolab deployed at the most downstream end of the weed choke creek section, just before it enters the mangrove zone, was interfered with by persons unknown and removed to the creek bank. We were not able to retrieve any data from this device.
Location of successfully deployed Hydrolabs

DS4 - 190 32’59.0”S 1470 15’07.2”E

DS10 - 190 31’20.9”S 1470 15’20.5”E

DS1 - 190 31’11.9”S 1470 15’10.1”E


The three sites from which data were retrieved are shown as DS1, DS4 and DS10 in Figure 1 (these are named for the Hydrolabs deployed there). DS4 was immediately upstream of any weed choked sections of creek and nominally represented the quality of water coming in to the lower Barrattas Creek from the irrigation area. DS1 and DS10 were located within weed choked sections of the creek, with one upstream and one downstream of the rail line (seen in Figure 1). Although located within heavily-choked sections of creek, the Hydrolab’s at these locations were deployed within open water at those locations, in order to assess the best possible scenario. These small open water areas within the weed choked creek reaches could potentially provide refuge for hypoxia-sensitive fish in these reaches.
The Hydrolab’s were deployed from 18 November 2011 to 16 December 2011, covering the period that was to include aerial herbicide spraying of aquatic weeds in the infested reach.
Manual spot readings of physico-chemical water quality were taken at various locations along the creek in November and December 2011. These locations were upstream, within and downstream, of the weed choke and represent a longitudinal survey of physico-chemical water quality along the creek. The upstream sites were at the highway crossings of both East and West Barratta creeks and the most upstream Hydrolab site. The within weed choke sites were located at the Hydrolab deployment sites DS1 and DS10, and the sites downstream of the weed choke, at the estuarine confluence are marked as PT1-5 are marked on Figure 1. The readings at these most downstream sites were taken in the middle of the day on 21 December 2011 at the bottom of low tide.


Figure 1. Locations of water quality readings in freshwater reaches

2.2.2 Fish Surveys in Freshwater Reaches
Fish surveys were conducted at one site upstream of the weed choked reaches and two sites within the weed-choked reaches. Fish surveys were undertaken using a Smith-Root 7.5GPP boat-mounted electrofisher. Fish caught were identified and released. Up to 20 individuals of each species were measured (standard length) before release. Fish observed in the water, but not captured were also recorded.
Site EB1, the upstream site, was located at S19 33'00.8 E147 14'58.9"

Sites EB2 and EB3, the weed-choke sites, were located adjacent to sites where the Hydrolabs were deployed.



2.3 Health of Upper Estuarine Habitats
2.3.1 Site Descriptions
Four study locations were selected as having a potential to monitor changes in Barratta and Barramundi Creeks that may stem from removal of the weed choke; Barratta upstream, Barratta downstream, Barramundi north and Barramundi south (Figure 2). Barratta upstream represented the upstream navigable extent of the Creek for the time of tide at which fauna were sampled. Both upstream and downstream locations overlapped with site locations from a previous study (Sheaves and Johnston 2009). Two upstream locations were selected in Barramundi Creek; Barramundi north at the navigable extent of one arm leading into saltpan and apparently unaffected by freshwater from the Barratta wetland, and Barramundi south, the arm which is thought to receive freshwater from the Barratta wetland as a result of the weed choke.
The three upstream locations were tidal although the Barramundi sites were at the upper extent of channelised tidal ingress, with only saltpans and mangrove forests further inland. All sites were flanked by mangroves, predominantly Avicennia marina in upstream sites and Rhizophora spp. in the downstream site.



Figure 2 Map of estuarine sites sampled in Barratta Creek and Barramundi Creek

2.3.2 Physical Data
Salinity, water temperature, dissolved oxygen (DO) saturation, turbidity and pH were recorded using an AquaRead 300 water quality meter. Readings were collected from each faunal sampling site (5 per location) at the commencement of sampling. Readings were collected from the surface at 20 cm depth and from a depth of 2 m or from 20 cm above the bottom when depth was less than 2 m. In addition, data were collected from each waypoint along the upstream-downstream gradient in Barratta Creek, from the boat ramp in Barramundi Creek and from a road crossing upstream of the Barramundi south faunal sampling site (Figure 2).

2.3.3 Nekton Survey
Nekton was sampled from five sites within each location. In each site ten cast net samples and four fish-crab trap samples were collected making 50 cast net and 20 trap samples per location. Cast nets were used to sample fish because they provide a rapid collection method that allows most fish to be recorded and returned to the water unharmed (Johnston and Sheaves 2008). Drawstring, monofilament cast nets, 2.4 m radius and 5 mm mesh were used for the study because these are particularly effective at representing the smaller component of the fish assemblages.
Antillean z-traps were used to sample mud crabs. Four traps were baited with pilchard and deployed prior to commencing cast net sampling in each site. Traps were collected once cast net sampling was completed at the site which provided soak times between 55 and 65 minutes. Crabs were counted and measured then released unharmed.
2.3.4 Data Analysis
Physical data were analysed using Principle Components Analysis based on a correlation matrix in Primer. This approach normalises data, removing biases of different measurement scales from the analysis to provide equal weighting for all variables. For comparative purposes data from an earlier study were accessed and presented graphically alongside data from the present study.
To account for differences in soak times among trap samples mud crab data were converted to catch per unit effort (CPUE) and analysed by Analysis of Variance (ANOVA). Data were log transformed prior to analysis to conform to assumptions of ANOVA. Fish and prawn data were pooled by site (10 replicate nets combined to a single sample) and log transformed prior to analysis. These data were analysed by Multi-dimensional Scaling (MDS) using Bray-Curtis distance in Primer. This approach emphasises assemblage composition rather than abundance but retains information about similarities and differences in abundance. To assist with interpretation and validation of apparent groupings the Simprov routine was utilised. Simprov is a similarity profiling technique that teats for structure in data. Where groupings of points are apparent in MDS plots Simprov provides a means of establishing if clustered points represent a coherent grouping.

3. RESULTS

3.1 Condition of Freshwater Reaches
3.1.1 Distribution of Hymenachne
In the May 2012 surveys, the distribution of hymenachne along East Barratta Creek from the Bruce Highway crossing to the old boat ramp was observed to be more or less continuous, although there were some sections near the highway crossing where it was absent for considerable lengths (Table 1; Figures 3 and 4; Figure 5, EB1; Appendix 1). Distribution was continuous and increasingly dominant from just upstream of the water pump, downstream to the old boat ramp (Figure 5, EB23, EB28). In some parts of this section, hymenachne had recently been treated with herbicides and what was formerly a continuous cover was, in most part, reduced to narrow stream edge strips or isolated in-stream patches (Fig. 5, EB11).
In the August 2012 surveys of West Barratta Creek, the distribution of hymenachne was more or less continuous from the Bruce Highway crossing (Table 1; Figures 6 and 7; Figure 8, WB2; Appendix 2), but intermittently absent from reaches where the creek was deeply incised with steep banks (Figure 8, WB7), and also absent from areas where saline influence was strongly developed (Fig. 8, WB 43, WB43). As with the East Barratta, hymenachne does not occur on mangrove banks, but on higher ground away from tidal and saline influences but still within the shelter of mangrove trees (Figure 5, EB, 23, EB28; Figure 10, WB49). In contrast to the East Barratta, the West Barratta has a greater number of ponded areas, some natural and some constructed; accordingly, many of these were highly infested with hymenachne (Figure 9, WB25, WB31).
3.1.2 Decline of Mangrove Vegetation
During the May 2012 surveys of East Barratta Creek, investigation into the decline of mangrove trees was also done. The limit of major saline influence was located and dead or senescent mangroves trees were observed (Figure 4; Figure 5, EB21, EB22). At this location, the only mangrove species present was Avicennia marina and numerous trees were dead. The most likely cause was the elevated flows of freshwater water smothering the pneumatophores (aerial breathing roots) of these trees. At this location, severe bank erosion was observed, most probably initiated by above-normal water levels from the damming event (Figure 3, EB22). Development of hymenachne and freshwater macrophytes on what was previously salt marsh, was also observed at the same location as the dead mangroves trees, confirming the conversion of this reach from upper estuarine to freshwater habitat.
Table 1. Hymenachne observation and monitoring sites on East Barratta Creek, in downstream order from

the Bruce Highway crossing [EB1] to the old boat ramp [EB31].




Site

Width (m)

Shade (%)

Slope (°)

Dominant vegetation

Major Weeds

EB1

5

0

0

Melaleuca

lantana

EB2

1

20

10

Melaleuca

lantana

EB3

1

20

2

Melaleuca

-

EB4

5

0

0

Melaleuca

-

EB5

3

0

0

Melaleuca

-

EB6

absent

n/a

20

Melaleuca

yellow oleander

EB7

absent

n/a

20

Melaleuca

yellow oleander

EB8

absent

n/a

2

Melaleuca

-

EB9

absent

n/a

2

Melaleuca

-

EB10

absent

n/a

5

Melaleuca

rubber vine

EB11

20

10

5

Melaleuca

-

EB12

10

10

5

Melaleuca

-

EB13

50

10

0

Melaleuca

-

EB14

5

0

5

Melaleuca

water hyacinth

EB15

10

0

5

Melaleuca

water hyacinth

EB16

7

5

5

Melaleuca

water hyacinth

EB17

4

5

5

Melaleuca

water hyacinth

EB18

30

5

5

Melaleuca

-

EB19

40

5

5

Melaleuca

-

EB20

70

5

5

Melaleuca/mangrove

-

EB21

70

5

5

Melaleuca/mangrove

-

EB22

50

0

0

mangrove

-

EB23

30

0

5

mangrove

parkinsonia

EB24

30

0

5

mangrove

typha

EB25

4

30

5

mangrove

rubber vine

EB26

40

0

0

mangrove

typha

EB27

40

0

0

mangrove

typha

EB28

40

5

5

mangrove

typha

EB29

10

5

5

mangrove

noogoora burr/typha

EB30

10

5

5

mangrove

typha

EB31

5

20

10

mangrove

typha


f:\application data\documents\images\barratta ck may2012\east barratta sites.jpg

Figure 3. Hymenachne distribution site locations on East Barratta Creek visited in May 2012.

f:\application data\documents\images\barratta ck may2012\east barratta saline limit.jpg Figure 4. Detail of East Barratta Creek map, showing the location of saline influence [EB20] and location of mangrove vegetation decline, mainly between sites EB21 and EB22.

f:\application data\documents\images\barratta ck may2012\eb1.jpg

f:\application data\documents\images\barratta ck may2012\eb11 (1).jpg

EB1, immediately downstream of Bruce Highway crossing, with minor in-stream infestations of hymenachne.

EB11, near the ‘water-pumping site’, start of significant infestation of hymenachne.

f:\application data\documents\images\barratta ck may2012\eb21.jpg

f:\application data\documents\images\barratta ck may2012\eb22 (3).jpg

EB21, saline influence limit and dead Avicennia.

EB22, erosion caused by hymenachne/water hyacinth dam.

f:\application data\documents\images\barratta ck may2012\eb23 (1).jpg

f:\application data\documents\images\barratta ck may2012\eb28) (2).jpg

EB23, dense hymenachne infestation upstream from Old Boat Ramp.

EB28, hymenachne infestation near the Old Boat Ramp.


Figure 5. Hymenachne sites, East Barratta Creek, May 2012.


Site

Width (m)

Shade (%)

Slope (°)

Dominant vegetation

Major Weeds

WB1

2

0

2

Melaleuca, Livistona decora

-

WB2

10

0

2

Melaleuca

-

WB3

absent







Melaleuca

salvinia

WB4

absent







Melaleuca, Livistona decora

rubber vine

WB5

2

0

0

Melaleuca

salvinia

WB6

absent







Melaleuca

salvinia

WB7

1

40

10

Melaleuca

salvinia

WB8

absent







Melaleuca, sedges

salvinia

WB9

absent







Melaleuca, Livistona decora

salvinia

WB10

50

0

0

Melaleuca

salvinia

WB11

2

0

0

Melaleuca

salvinia

WB12

2

0

0

Melaleuca

salvinia

WB13

10

0

0

Melaleuca

salvinia

WB14

2

0

0

Melaleuca

rubber vine

WB15

10

10

0

Melaleuca

salvinia

WB16

1

10

5

Melaleuca

salvinia

WB17

1

5

5

Melaleuca

salvinia

WB18

1

20

0

Melaleuca

salvinia

WB19

2

20

0

Melaleuca

salvinia

WB20

1

5

0

Melaleuca, Livistona decora

salvinia

WB21

1

5

0

sedges, Melaleuca

salvinia

WB22

absent







Melaleuca, Livistona decora

salvinia

WB23

2

5

2

Melaleuca, Potamogeton

-

WB24

2

5

2

Melaleuca

salvinia

WB25

2

5

2

sedges

salvinia, rubber vine

WB26

absent







Persicaria, Eucalyptus

salvinia

WB27

absent







Melaleuca

lantana

WB28

2

5

5

Melaleuca

lantana

WB29

absent







sedges

-

WB30

30

5

5

sedges, Melaleuca

-

WB31

100

0

2

Melaleuca

-

WB32

absent







sedges, Potamogeton

salvinia

WB33

absent







Melaleuca, Livistona decora

-

WB34

absent







Schoenoplectus

-

WB35

absent







Schoenoplectus

-

WB36

absent







Sporobolus virginicus, Sarcornia, Portulaca

-

WB37

2

5

2

Melaleuca (senescent)

rubber vine

WB38

absent







Melaleuca (senescent)

salvinia, typha

WB39

5

0

2

sedges, Melaleuca

typha

WB40

30

0

0

Melaleuca

salvinia

WB41

2

0

0

Melaleuca

paragrass

WB42

20

0

0

sedges

-

WB43

20

0

0

Schoenoplectus, Nymphaea

-

WB44

absent







Schoenoplectus, Melaleuca

-

WB45

absent







Melaleuca

salvinia

WB46

10

0

0

Schoenoplectus, Nymphaea

-

WB47

20

0

0

Schoenoplectus, Nymphaea

-

WB48

2

0

0

-

-

WB49

2

10

2

mangroves, Schoenoplectus

typha, water hyacinth

WB50

1

20

5

mangroves

-

WB51

absent







mangroves

-

Table 2. Hymenachne observation and monitoring sites on West Barratta Ck, listed downstream from the Bruce Highway crossing (WB1) to near Jerona (WB51).

3.1.3 Effect of Hymenachne and Other Weeds on Waterflow
The environmental impacts of hymenachne are well documented (DRNMW 2006; WONS 2011). Where established, hymenachne alters the environment by out-competing and eliminating other species, by affecting water quality by cover, and by providing opportunities for erosion by way of debris accumulation during floods and periods of high water flow. Debris dams also influence the time period that freshwater is ‘backed-up’. This has two impacts: firstly, riparian vegetation becomes waterlogged and is prone to oxygen deprivation and ‘drowning’; secondly, the balance between freshwater/saline conditions is skewed toward the former, thus impacting on saline dependent/tolerant vegetation. All of these situations are presently active in the Barratta creek system, with both hymenachne and water hyacinth being the primary causes.
Management of both hymenachne and water hyacinth is difficult, considering the inaccessibility of infestations during periods of high growth rate and wide-scale establishment. In the Barratta Creek system, physical removal appears to be the most practical option. The application of herbicides may also be appropriate, as this has proven effective in some sections of East Barratta Creek. Hymenachne has a preference for full sun or only slightly shaded environments. This broadly indicates that the presence of riparian trees restricts the establishment of populations in well-shaded areas, and that maintaining the integrity of riparian shading should be a part of long-term control in channelized reaches. On the floodplain, in wetlands, other management methods, such as fire and controlled grazing may be more useful (Veitch et al. 2007). In the interim, annual application of herbicide will be required to keep the infestations at a manageable level.

3.1.4 Melaleuca Decline
During the August 2012 surveys of West Barratta, no observations were made of declining mangroves. However, areas of dead and/or senescent melaleuca (Melaleuca leucadendra), south of the railway line, can be attributed to an interruption in drainage associated with the ramparts of the railway line (Figure 9, WB37). This situation appears unrelated to the presence of hymenachne, either in growth or by the creation of a dam during periods of high water flow.


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