Leaf Litter Decomposition and Utilisation by Macroinvertebrates in a Central Victorian River in Australia
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Federation ResearchOnline Research Reports Leaf litter decomposition and utilisation by macroinvertebrates in a central Victorian river in Australia JMCK Jayawardana1, 2, Martin Westbrooke1, Michael Wilson3 1School of Science and Engineering, University of Ballarat, Vic 3353, Australia 2Department of Natural Resources, Faculty of Applied Sciences, Sabaragamuwa University Belihuloya, Sri Lanka. Email: [email protected] 3 Murray Darling Basin Commission, GPO Box 409, Canberra, ACT 2601, Australia Abstract Th is study suggested that long-term persistence of willow roots can provide a positive eff ect on aquatic com- munities until the new native vegetation cover establishes. Leaf type has no signifi cant infl uence over taxa richness; however their availability and persistence in the system has a signifi cant eff ect on macroinvertebrate abundance in these streams. A combination of Phragmites reeds with Leptospermum and Callistemon shrubs in revegetation programs will ensure a persistent supply of leaf litter to macroinvertebrate communities in these streams thus should be retained until native canopy cover eg. Eucalyptus spp. is re-established. (Th e Victorian Naturalist 127 (4) 2010, 104–114) Keywords: Leaf litter, exotic, willow, Phragmites, Eucalyptus Introduction Th e landscapes of central Victoria are largely vol- Redistribution of Phragmites in rivers managed canic in origin and highly modifi ed through clear- by irrigation has been observed in south- eastern ing for agriculture. Exotic willows Salix fragilis Australia (Roberts 2000). However, quantitative have successfully colonised and become natural- studies on the eff ects of this on river health and ised taxa in many riverbanks in these landscapes aquatic biodiversity are limited (Roberts 2000). (Ladson et al. 1997). It is estimated that willows In addition, Phragmites is sometimes used dur- have spread across approximately 30 000 km of ing revegetation, increasing the likelihood it will the 68 000 km river frontage in Victoria (Lad- be a coloniser following willow removal. Native son et al. 1997). Willows are considered a Weed shrubs such as Leptospermum spp. and Calliste- of National Signifi cance in Australia and willow mon spp. are common in many temperate Aus- management strategies recommend their removal tralian streams and are a signifi cant component as the preferred and generally only management in the riparian zone of streams where willows are option (National Weeds Strategy Executive Com- removed. mittee 2000). Revegetation is encouraged follow- A key diff erence between willows and the na- ing removal. Th erefore, the sequence of riparian tive Australian riparian vegetation is the timing changes is: willow lined streams → open streams and quality of leaf fall (Pidgeon and Cairns 1981; → native vegetation lined streams. Decades will Yeates 1994; Frankenberg 1995). It has been be required to achieve a canopy cover of native argued that a change in the timing or quality species equivalent to the preceding willow cover. of litter fall resulting from a change in riparian Phragmites australis is one of the common native vegetation phenology would aff ect stream en- reeds of open streams and wetlands worldwide ergetics and be refl ected in the composition of (Sainty and Jacobs 1981). Th ere is increasing evi- stream biota (Campbell 1993; Schulze and Walk- dence to suggest that riparian disturbance, altera- er 1997). Th ese were attributed to the diff erences tion of natural hydrologic regime, soil salinisation in breakdown rates, palatability and chemical and increased sedimentation favour invasion and composition of leaf types (Schulze and Walker continued spread of Phragmites in lotic systems 1997; Irons et al. 1988; Campbell and Fuchshu- (McNabb and Batterson 1991; Saltonstall 2003). ber 1995). A study by Yeates and Barmuta (1999) Invasion of Phragmites in open reaches with low supported the idea that willow leaves were more riparian vegetation cover has been observed in palatable and preferred by macroinvertebrates many river catchments in Victoria (CALP 1997). than the leaves of Manna Gum Eucalyptus vimi- 104 Th e Victorian Naturalist Research Reports nalis. However, the availability of leaf litter was camaldulensis and native reed Phragmites australis limited during some seasons in willow-lined were investigated. Th e outcome of this study will streams because of the seasonality of litter-fall provide important information for management pattern of willows. It has been found that small of exotic species and revegetation programs. streams that rely entirely on willows for their leaf inputs might run short of coarse particulate food Study site matter during winter (Pidgeon and Cairns 1981; Moorabool River catchment covers approxi- Cummins et al. 1989). Some authors suggest that mately 148 000 ha. Over 75% of the catch- the greater palatability of willow leaves com- ment is used for agriculture, either grazing or pared to native leaves causes a short term boost broad-acre cropping (Department of Water of macroinvertebrates under willow lined chan- Resources Victoria 1990). Th ere are three areas nels during autumn when willows shed most of of mixed-species forest in the middle reaches their leaves (Yeates and Barmuta 1999). Phrag- of the Moorabool River. Willows are commonly mites australis is lightly grazed in the living state, distributed along the riparian zone, particularly and the greatest part of the primary production in the upper catchment. In the middle sections, ultimately enters detrital systems (Imhof 1973). willow removal programs have been under- Mathews and Kowalczewski (1969) and Th omas taken. Th e study site was located near Mor- risons on the Moorabool River (latitude 370 6’ (1970) reported a faster decomposition rate for 0 tree leaves than emergent macrophytes such as S., longitude 144 2’E., altitude 442 m) where Phragmites. No information exists on decom- willow removal has been carried out (Fig. 1). position and macroinvertebrate use of leaves Th is section of the river is in moderate condi- of common shrubs such as Leptospermum and tion according to criteria of ISC classifi cation Callistemon spp. However, these leaves are scle- (Index of Stream Condition) and has peren- rophyllous and frequently aromatic (Walsh and nial fl ow (Department of Sustainability and Entwisle 1996; Lis-Balchin et al. 2000), suggest- Environment 2005). Th e experiment was con- ing a high content of lignin and herbivore deter- ducted from early April (mid autumn) to the rents. Th ese compounds may act as deterrents end of July (mid winter) 2005. Th e stream fl ow for macroinvertebrate and fungal activity lead- remained relatively constant throughout the ing to the slower decomposition of leaves. experimental period, ranging from 0.01 to 0.15 Another important habitat structure remaining m/sec. Channel depth and width ranged from in streams from which willows have been removed 18 cm to 30 cm and 12 to 14 m. Dissolved oxy- are willow root mats, since stumps of willows are gen concentration and pH ranged from 7.4 to oft en left aft er removing the upper parts. Root 7.9 mg/L and 7.4 to 7.9 during the study period. Temperature and conductivity ranged from 6 to decomposition is an oft en ignored, yet potentially 0 important regulator of carbon and nutrient cycling 14 C and 287 to 245 μS/cm respectively. in terrestrial systems (Ostertag and Hobbie 1999). Materials and Methods It has been observed that willow roots remain in For the experiement, fresh willow, Eucalyptus, streams long aft er the trees have been cut down. Phragmites, Leptospermum and Callistemon Th is suggests that willow roots have slow decom- leaves were collected from plants along with position rates but empirical evidence to support fresh willow roots. Aft er collecting, leaves and this observation is scant. It appears the eff ect of leaf willow roots were air dried for one week until a litter input from such exotic and native vegetation constant weight was attained. Roots were rinsed successional processes may have important infl u- well to remove attached mineral particles before ences on the macroinvertebrate communities and drying. Fift een grams of dry leaves from each energy transfer process of these streams. However, leaf type and roots were put into 5 mm mesh no comprehensive study has been carried out to bags separately and tied to nylon lines in a ran- investigate the eff ects of such vegetation changes dom order. Th is mesh size was selected to allow on leaf litter availability and macroinvertebrate macroinvertebrates to enter the mesh bags for communities in Australia. Th erefore, decompo- feeding and also to reduce leaf loss through the sition rates and macroinvertebrate colonisation net. Each nylon line was attached to six mesh of leaves and roots of exotic willow, Salix fragilis, bags containing fi ve types of leaves and willow leaves of native shrub species Leptospermum lani- roots. Th e nylon lines were attached to bricks gerum and Callistemon paludosus, a native ripar- positioned one metre apart, in a homogeneous ian woody tree the River Red Gum Eucalyptus Vol 127 (4) 2010 105 Research Reports Fig. 1. Location of study sites. section of the stream bed. Th ree replicate sam- was dried for fi ve days until constant weight was ples from each leaf type and root packs were attained then dry weight was recorded. randomly removed aft er 7, 14, 28, 42, 56, 70, 84, Leaf/root weight loss with time 98 and 112 days. Care was taken to avoid losing Decomposition rate of leaves and roots is based bag contents while removing them from the wa- on ‘mass loss of leaves/roots from initial mass’ ter. Water quality parameters were also recorded as defi ned by Hofsten and Edberg (1972). Leaf when removing leaves. Contents of the mesh pack processing as measured by weight loss of bags were put in plastic trays and macroinverte- packs through time was estimated with a sim- brates were separated and preserved in 70% al- ple exponential decay model (Petersen and cohol for later identifi cation.