final report knowledge for managing Australian landscapes Assessing the potential for algal blooms in clear water phase tropical rivers Project number: UAD21 Principal Investigator Associate Professor George Ganf University of Adelaide Email: [email protected] Dr Naomi Rea Charles Darwin University Email: [email protected] Published by: Postal address: GPO Box 2182, Canberra ACT 2601 Office location: Level 1, The Phoenix, 86-88 Northbourne Ave, Braddon ACT Telephone: 02 6263 6000 Facsimile: 02 6263 6099 Email: [email protected] final report Internet: www.lwa.gov.au Land & Water Australia © January 2006 Disclaimer: The information contained in this publication is intended for general use, to assist public knowledge and discussion and to help improve the sustainable management of land, water and vegetation. It includes general statements based on scientific research. Readers are advised and need to be aware that this information may be incomplete or unsuitable for use in specific situations. Before taking any action or decision based on the information in this publication, readers should seek expert professional, scientific and technical advice and form their own view of the applicability and correctness of the information. To the extent permitted by law, the Commonwealth of Australia, Land & Water Australia (including its employees and consultants), and the authors of this publication do not assume liability of any kind whatsoever resulting from any person’s use or reliance upon the content of this publication. Assessing the potential for algal blooms in clear water phase tropical rivers final report Final Report January 2006 Project Reference: UAD21 Program: National Rivers Consortium. Tropical Rivers Program Mini-call Host Organisation: University of Adelaide Investigators: Assoc. Prof. George Ganf (Univ. of Adelaide) Dr Naomi Rea (Charles Darwin Univ.) Correspondence: [email protected] [email protected] CONTENTS 1. Introduction 1.1 Aims 2. Study sites 3. Regional site hydrology and land use 3.1 Darwin and Bynoe Harbour Catchments 3.2 Daly and Roper River Catchments 4. Methods Sample collection Analysis 4.1 Phyto-Pam measurements Chlorophyll calibration Chlorophyll concentrations Quantum Yield Electron Transport Activity Nutrient enrichment experiments Photo-chemical and non-photochemical quenching 5. Results 5.1 Total Chlorophyll and distribution across blue green, green and brown algae Darwin and Bynoe Harbour tributaries Daly and Roper River tributaries 5.2 Algal response to nutrient enrichment Howard (March / April) Blackmore (March 2005) Elizabeth (March 2005) Katherine (April 2005) Daly (May / June 2005) Charlotte (July 2005) Darwin (July 2005) Elizabeth (July 2005) Howard (July 2005) Roper (August 2005) Daly (August 2005) Katherine (August 2005) 5.3 Growth Rates and River Discharge Rates 5.4 Algal growth response to light and nutrients 5.5 Response of Chlorella to uranium 4 6. Discussion 6.1 Chlorophyll as an index of river health 6.2 Predicting potential river health using chlorophyll 6.3 Biologically available N and P 6.4 Target nutrient concentrations 6.5 Light as limiting factors for algal blooms 6.6 River length and discharge Concluding remarks Acknowledgements The facilities provided by Environmental Research Institute of the Supervising Scientist (eriss) to GGG are greatly appreciated and contributed enormously to the smooth running of the project. In addition, we wish to thanks members of staff of eriss for their friendly advice and help in many matters. The project was undertaken whilst GGG was on leave from the University of Adelaide under the University’s Special Studies Program. Land and Water Australia (UAD21) provided financial support for the project. Citation: Ganf GG and Rea N (2006). Assessing the potential for algal blooms in clear water phase tropical rivers. Final Milestone Report to Land and Water Australia, January 2006. 5 1. Introduction Algal blooms commonly occur in rivers across southern Australia and worldwide. Blooms and their associated biota cause taste and odour problems that are a constant source of complaints to water authorities. Blooms dominated by cyanobacteria or blue green algae are of economic and environmental concern because estimates suggest that 60-70% are toxic. The health risks associated with toxic blooms may lead to the closure of rivers for recreational use and disrupt water supplies for domestic, industrial and irrigation purposes. The formation of blooms, or dense algal populations, requires a supply of nutrients and energy so that the products of photosynthesis may be converted into algal biomass. The species composition, net rate of growth, final crop density all depend upon an interplay between temperature, nutrient availability and preference, thermal stratification and flow. Biological characteristics such as buoyancy regulation and susceptibility to grazing (eg size, taste) also play an important role. Factors leading to algal populations are reviewed by Oliver and Ganf (2000) who placed emphasis on a) the supply of two nutrients, phosphorus and nitrogen, and b) the depth of the surface mixed layer in relation to the depth of the euphotic zone. Their conceptual model was directed more towards turbid lakes and reservoirs than to clear, flowing rivers and they do not explore the interaction between algal growth rate, discharge and the potential for algal populations to persist in flowing rivers where downstream advection may exceed algal growth rates (Spiers and Gurney 2001). The rivers of northern Australia and particularly those in the Top End of the Northern Territory are subject to major seasonal changes in flow and inter-annual variability. For example, the Daly River experiences dry season discharge rates of 2 to 80 m3 s-1 (Webster et al. 2005). The ecological character of this river is shaped by the annual changes in discharge. High wet season flows reset the ecological clock (Webster et al. 2005) and can scour the river of macrophyte beds (Rea et al. 2003). During the dry season, spring water maintains flow with different water chemistry from the rainfall run- off that constitutes wet season flow. Based upon a number of biophysical observations, Rea et al. (2003) and Webster et al. (2005) suggest that the net accumulation of plant biomass in the river is limited by nutrient availability. Although dry season flows favour macrophyte and phytoplankton growth, low concentrations of available essential nutrients in the water and in the tissues of Vallisneria nana, suggest that growth at this time of year is constrained by the nutrient poor groundwater that keeps the river flowing. Blanch et al. (2005) identify river hydrology and chemistry as central to the significant conservation values of the Daly River, including fish and turtle, diversity and abundance. Across the Top End, irrigated agriculture and the concomitant change in land use have been identified as a threat to the regions’ clear water rivers (Erskine et al. 2003, Blanch et al. 2005). Evidence from southern Australia strongly supports the hypothesis that changes in catchment use will give rise to major water quality problems because of altered river hydrology, increased nutrient loads and decreased base flows. Such changes could give rise to algal blooms that would impact upon important commercial and recreational fisheries, alter the balance between the major primary producers 6 (aquatic macrophytes, benthic and pelagic algae) and decrease the mobility and fecundity of icon species such as freshwater turtles. This project built on the Daly River studies of Rea et al. (2003) and Webster et al. (2005), expanding the research to several other catchments and rivers in the Top End. An initial desk-top survey identified adjacent catchments that could be used to contrast the impact of different levels of land use on tropical rivers, in terms of algal concentrations and growth. Streams in the modified catchment of Darwin Harbour could be compared with those in the relatively unimpacted catchment of Bynoe Harbour: the rivers in both catchments are <100km in length. A similar difference between the Daly and Roper River catchments was identified as an opportunity to investigate potential impacts on longer and larger rivers. Despite the numerous rivers in both regions, there is very little published literature on algae and nutrient conditions outside the Daly River. Agriculture development and population growth is occurring across the Top End, especially in the Darwin Harbour and Daly River catchments. The Daly River catchment in the lower and upper sections is forecast to experience a significant increase in irrigated agriculture (Erskine et al. 2003). Although the middle reaches of the Daly River were the subject of environmental flow studies in 2000-2002, rivers further up the catchment, such as the Katherine, Edith, Cullen, Fergusson, which drain the Arnhem Land Plateau, have not received the same attention: the same applies to the King and Dry River’s that drain pastoral lands to the south. The Katherine is of particular significance because it provides the drinking water for the township of Katherine. Rivers such as the Edith and Maude Creek may feel the impact of mining as well as agriculture. As with the Daly, the Roper River drains part of the Arnhem Land Plateau but flows eastwards, instead of westwards, to the Gulf of Carpentaria. The Roper catchment around Mataranka is also experiencing an emerging agricultural industry. The factors promoting algal blooms are well