ENVIRONMENT REPORT MONITORING RIVER NUTRIENT LOADS TO THE GIPPSLAND LAKES 2006–07 Report to the Gippsland Lakes Task Force Task RCIP EG-0607-04.018 Publication 1271 February 2009 1 MONITORING RIVER NUTRIENT LOADS TO THE GIPPSLAND LAKES 2006–07 SUMMARY bushfires in the upper catchments and to several major flood events. This report presents the results of a monitoring • Monitoring of nutrient loads immediately program designed to assess the loads of nutrients downstream of the bushfire-affected areas on the entering the Gippsland Lakes during 2006—07. EPA Thomson, Macalister, Avon and Mitchell Rivers Victoria conducted the monitoring program for the confirmed that these areas were a major source Gippsland Lakes and Catchment Task Force. of nutrients to the Gippsland Lakes. Lake The monitoring program measured the loads of the two Glenmaggie appears to have retained a main nutrients (phosphorus and nitrogen) entering the considerable proportion of the nutrients Gippsland Lakes from the six major rivers that drain the transported by the Macalister River following the catchment of the lakes over the 12-month period from fires, reducing the load that would have otherwise 1 July 2006 to 30 June 2007. This report describes the entered the lakes. nutrient loads contributed by the individual rivers, irrigation drains and major flood events. A number of catchments within the region were affected by major bushfires in December 2006 and a major flood (a one-in-100–year event) that commenced in June 2007 and continued into July. While the flood extended beyond the nominal study period, the magnitude of this event warranted a separate assessment of the nutrient loads over the full period of the event. Nutrient loads up to 30 June and the loads associated with the flood event are reported in section 4.3. Additional nutrient load measurements were taken downstream of the fire-affected catchments for the period February 2007 to February 2008. These measurements assist in understanding the significance of the fire-affected catchments as sources of nutrients. The main findings presented in this report are summarised as follows: • The estimated nutrient loads entering the Gippsland Lakes from the six main rivers and Macalister Irrigation District irrigation drains (phosphorus only) in the period 1 July 2006 to 30 June 2007 were: { total nitrogen — 2731 tonnes { total phosphorus — 376 tonnes. • The majority of the nutrients were transported during two flood events in June 2007. • The estimated loads occurring during the floods of June/July 20071 were: { total nitrogen — 3096 tonnes { total phosphorus — 329 tonnes. • The three western rivers contributed less nutrient load than the three eastern rivers. This may reflect differences in rainfall across catchments and the possible role of Lake Glenmaggie in retaining nutrient loads transported by the Macalister River. • The nutrient loads entering the Gippsland Lakes during 2006—07 were higher than in the past few years and this can be attributed to the severe 1 The estimates for the flood event include loads from July 2007 and there are not directly comparable with the loads presented above for the 2006—07 year. 2 MONITORING RIVER NUTRIENT LOADS TO THE GIPPSLAND LAKES 2006–07 1. BACKGROUND The Gippsland Lakes make up an important ecosystem in terms of environmental, economic, The Gippsland Lakes are a series of large, estuarine cultural and social values. Its wetlands are listed lakes situated in the south-eastern corner of Australia under a number international conventions and with a total area of 364 km2 (Figure 1). The lakes are treaties, including the Ramsar convention, the Japan generally shallow, with Lake Wellington in the west Australia Migratory Bird Agreement (JAMBA) and the having an average depth of 2.6 m, Lake Victoria 4.8 m China Australia Migratory Bird Agreement (CAMBA) and Lake King 5.4 m (Webster et al. 2001). At the (Anon. 2003). The Gippsland Lakes are recognized as eastern end of the Gippsland Lakes is a man-made an important nursery ground for a diverse selection channel (Lakes Entrance). Six major rivers drain a total of aquatic species, some with commercial importance catchment area of 20,600 km2, which represents about (Rigby 1982, Ramm 1983, Coutin et al. 1996). nine per cent of the total land area of Victoria (Webster The Gippsland Lakes are an important tourist et al. 2001). destination and tourism is an important element in economic and employment growth of the region (Anon. 2005). Lake King Lake Victoria Lakes Entrance Lake Wellington Bass Straight Figure 1. Location of Gippsland Lakes, Victoria and monitoring stations Figure 1: Location of the Gippsland Lakes, Victoria, Australia. 3 MONITORING RIVER NUTRIENT LOADS TO THE GIPPSLAND LAKES 2006–07 2. WHY MEASURE NUTRIENT LOADS In response, nutrient reduction programs have been initiated throughout the Gippsland region. In addition, ENTERING THE GIPPSLAND LAKES? a more intensive monitoring program was initiated that measures both low and high-flow events to more A number of reviews have considered the major accurately estimate nutrient loads to the Gippsland environmental pressures and associated problems that Lakes. This report presents the results of this more pose a threat to the integrity of the Gippsland Lakes intensive load monitoring program. ecosystem (Harris et al. 1998, Webster et al. 2001). The riverine nutrient load monitoring program The catchment surrounding the Gippsland Lakes has provides an annual measure of nutrient loads to the significantly altered since the settlement of Europeans Gippsland Lakes. These annual estimates can be in the mid-19th century. For example, forests have been compared to past annual loads to see whether cleared to make way for agriculture, mining and nutrient loads are decreasing or not. Variability urbanisation. As a result more nutrients, toxicants and between years means that any evaluation needs to sediment have been washed from the catchment, consider the long-term trend in nutrient loads rather through the rivers and into the lakes. Of considerable than simply comparing one year with the previous environmental and economic concern is the frequency one. and intensity of cyanobacterial blooms. The annual estimate of nutrient loads provides an Increased nutrient loads to the Gippsland Lakes have indicator for environmental managers and funding led to the degradation of the ecosystem. Impacts bodies in assessing whether management actions are include increased algal blooms and decreases in on track to meet the established nutrient reduction seagrass and fish populations. Dissolved oxygen targets. concentrations in the lakes are also affected by increased nutrient loads (Harris et al. 1998). The program is made possible by the continuing commitment of the Victorian State Government The Gippsland Lakes Future Directions and Action Plan through the Gippsland Lakes Rescue Package (RCIP (GLFD&AP 2002) established a target of a 40 per cent EG–0607–04.018). This program operates in reduction in nutrient loads (total nitrogen and total cooperation with the Gippsland Regional Water phosphorus) entering the Gippsland Lakes by 2022. This Monitoring Partnership (GRWMP). reduction is benchmarked against nutrient loads estimated during the CSIRO Lakes Modelling Project (Webster et al. 2001). 4 MONITORING RIVER NUTRIENT LOADS TO THE GIPPSLAND LAKES 2006–07 3 MONITORING AND ESTIMATING LOADS Table 1: Site description and percentage of catchment captured by the nutrient loads monitoring program 3.1 Where did we measure? Percentage Site The Gippsland Lakes catchment contains six major River Location catchment captured number rivers that drain into the lakes (Figure 1). (from Scanlon 2007) Three of these rivers (Thomson including the Macalister 223209 Tambo Battens Landing 77 River, Latrobe and Avon) are situated at the western end of the lakes and drain into Lake Wellington. These 223210 Nicholson Sarsfield 77 rivers also receive drainage from a large proportion of the Macalister Irrigation District (MID). 224217 Mitchell Rosehill 91 The three eastern rivers (Mitchell, Nicholson and 225232 Thomson Bundalaguah 80 Tambo) drain into Lake King towards the eastern end of (Incl. 100% the lakes. Macalister R) Monitoring sites were established in the lower reaches 225234 Avon Clyde Bank 80 of each river in 2004 and 2005 (Figure 2). These sites were chosen on the following criteria: 226227 Latrobe Kilmany South 95 • availability of continuous flow data • capacity to capture nutrient run-off from a high In February 2007 additional monitoring sites were proportion of the catchment established to assess the impact of fire-affected • logistics (occupational health & safety, site access catchments. The results of this monitoring are and establishment costs etc) described in Section 4.5. This additional monitoring • availability of comparable historical data. was not funded by the Gippsland Task Force, but the Site details and the proportion of each catchment results are presented in this report for completeness. captured by each monitoring site are summarised in table 1. Nicholson River (Sarsfield) Tambo River Mitchell River (Rosehill) (Battens Landing) Lake King Lake Victoria Avon River (Clydebank) Thomson River (Bundalaguah) Lake Wellington Latrobe River (Kilmany south) Figure 2: Monitoring site locations and site names. 5 MONITORING RIVER NUTRIENT LOADS TO THE GIPPSLAND LAKES 2006–07 3.2 How are the nutrients measured? Data from this monitoring program is provided to the Victorian Water Data Warehouse