Estuarine, Coastal and Shelf Science 92 (2011) 59e69 Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss Influence of intermittent estuary outflow on coastal sediments of adjacent sandy beaches Jessica L. McKenzie*, Gerry P. Quinn, Ty G. Matthews, Jan Barton, Alecia Bellgrove School of Life and Environmental Sciences, Deakin University, P.O. Box 423, Warrnambool, Victoria 3280, Australia article info abstract Article history: Outflows from estuaries potentially contribute to the productivity of adjacent coastal waters, although Received 13 April 2010 most previous work has been on estuaries with considerable river discharge. We investigated the Accepted 12 December 2010 influence of estuary outflow on aspects of coastal sediments adjacent to two seasonally intermittent Available online 23 December 2010 estuaries, the Curdies and Anglesea Rivers, in southwest Victoria, Australia. For each estuary, we measured sediment organic matter, microphytobenthic chlorophyll a and microbial utilization of carbon Keywords: sources at three locations associated with each estuary: (1) inside estuary mouth, (2) estuary swash and estuary (3) control swash (an open beach distant from any estuarine influences). Sampling occurred one week mouth opening fi fl sediment before and at one and nine weeks after both an arti cial mouth opening and a separate natural ood at fi BIOLOG EcoPlates both estuaries. Signi cant temporal changes were detected for all three variables at the estuary mouth microphytobenthos and estuary swash but the direction of change was inconsistent across the two estuaries and between the organic matter artificial mouth opening and natural flood. Organic matter in both estuaries showed no difference after the artificial mouth openings. Only Anglesea showed an increase in organic matter in the estuary mouth and estuary swash after the floods. Microphytobenthic chlorophyll a concentrations were highest when the estuary mouths were closed. Concentrations decreased at all locations at Curdies after the mouth was artificially opened. The estuary mouth at Anglesea sustained high chlorophyll concentrations and the estuary swash increased one week post artificial opening. The flood event resulted in an increase in chlorophyll a at the estuary mouth and swash at both estuaries, one week post flood. At Curdies, the microbial utilization of different carbon sources changed after both mouth events; estuary mouth and estuary swash showed similar patterns at one and nine weeks post opening. At Anglesea, the bacteria utilized different carbon sources between locations and the only significant interaction between location and time was post flood with change in carbon sources utilized by bacteria in the estuary mouth and estuary swash for one and nine weeks post flood. The southern coastline of Australia is characterized by estuaries with small catchments. This study highlights the spatial and temporal variability in the effects of the output of relatively small, intermittent estuaries on coastal sediment of adjacent beaches, particularly during prolonged periods of drought. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction into offshore waters in the form of a plume. The importance of these plumes has been studied for large rivers (e.g. Amazon, Mis- Estuaries are dynamic environments and form an integral part sissippi) and have shown to increase primary productivity by of the coastal zone. Lying at the interface between marine, fresh- delivering ‘fresh’ nutrient loads and depositing organic material water and terrestrial systems, estuaries are well known for being from the catchment to coastal waters (Calef and Grice, 1967; Trefry highly productive environments, which provide essential nursery et al., 1994; Grimes and Kingsford, 1996; Smith and Demaster, 1996; habitats for many fish species and feeding grounds for numerous Lohrenz et al., 1999; Perissinotto et al., 2000; Rabalais et al., 2000; bird species (Robertson and Duke, 1987; Laegdsgaard and Johnson, Dagg and Breed, 2003; Liu and Dagg, 2003; Dagg et al., 2004; Green 1995; Grimes and Kingsford, 1996; Nagelkerken et al., 2001; Dagg et al., 2006; Schlacher et al., 2009). and Breed, 2003; McLusky and Elliott, 2004; Smith and Hindell, In temperate Australia and South Africa, seasonal or intermit- 2005; Becker and Laurenson, 2008). Estuary outflow discharges tently open estuaries are common; such systems can experience separation from the ocean by the presence of a sandbar at the * Corresponding author. mouth, particularly during periods of low rainfall and high seas E-mail address: [email protected] (J.L. McKenzie). (Eyre and France, 1997; Perissinotto et al., 2000; Cowley et al., 2001; 0272-7714/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2010.12.015 60 J.L. McKenzie et al. / Estuarine, Coastal and Shelf Science 92 (2011) 59e69 Barton and Sherwood, 2004; Harrison, 2004; Gladstone et al., 2006; have shown to be enriched in nutrients (EPA, 2000; Sherwood et al., Haines et al., 2006; Hastie and Smith, 2006; Matthews, 2006; Pope, 2008). These estuaries have demonstrated high nutrient levels in the 2006; Allan and Froneman, 2008; Anandraj et al., 2008). In these water column particularly during autumn and winter (EPA, 2000), types of estuaries prolonged mouth closure is common, especially with nitrogen and phosphorus exceeding the values recommended during droughts, and therefore the estuary might be artificially in the ANZECC and ARMCANZ (2000) guidelines of 0.08 mg/L and opened to protect assets of adjacent landholders from flooding. 0.035 mg/L respectively (ANZECC and ARMCANZ, 2000; Sherwood Artificial opening of the mouth usually involves digging a trench et al., 2008). These data suggest that estuaries are releasing high through the sandbar at the mouth and re-linking the estuary to the nutrient loads into coastal waters, providing the opportunity to ocean (Barton and Sherwood, 2004). potentially detect an influence on organic matter, micro- In Australia, although small estuaries discharging onto open phytobenthos and bacteria communities of coastal sediments on coastlines are very common, few studies have investigated plume adjacent sandy beaches. traits and their influence on adjacent coasts for these smaller systems The influences of artificial estuary mouth openings and natural (Kingsford and Suthers, 1994; Gaston et al., 2006; Ostrander et al., floods on sediment organic matter, microphytobenthos and micro- 2008; Connolly et al., 2009; Schlacher et al., 2009). Most studies biota were examined at two intermittent estuaries located in that have investigated the effect of estuary plumes of larger rivers on southwest Victoria, Australia (Fig. 1). Along this coast, strong south- coastal waters have focused on fish recruitment, water quality and easterly winds are common during the winter and spring when macroinvertebrate assemblages (Grimes and Finucane, 1991; estuaries are likely to be open, meaning inshore currents and Kingsford and Suthers, 1994; Grimes and Kingsford, 1996; Eyre and potential estuary plumes travel to the east. To avoid the influence of France, 1997; Lohrenz et al., 1999; Cowley et al., 2001; Froneman, the plume from south-easterly prevailing currents, control sites 2002; Gladstone et al., 2006; Hermand et al., 2008; Chumen et al., were selected at least 1 km west of the estuary mouths, with no 2009). This study is one of the first to be conducted on intermittent freshwater discharging onto the beaches. The Curdies estuary estuaries in Australia, as previous studies have examined plume traits (14252046"E, 3836036"S) is part of a catchment covering an area of of small permanently open estuaries (Gaston et al., 2006; Connolly w1200 km2, and is one of the largest estuaries in Victoria, extending et al., 2009; Schlacher and Connolly, 2009; Schlacher et al., 2009). w16 km (Sherwood et al., 2008), discharging onto a high energy Preliminary data showed that macroinvertebrates were not suitable coast at Peterborough. The widest section of the estuary is approx- for use in the present study because they were either rare or absent in imately 300 m. Most of the catchment is used for agriculture (90%), the shallow subtidal zones of the highly exposed sandy beaches onto with only a small portion of native vegetation and forest remaining which the estuaries opened (unpublished data). Sampling of fish was (Barton and Sherwood, 2004; Sherwood et al., 2008). Generally, the impractical because of the exposed nature of the shores and there mouth closes over in the drier months, December to June (Barton were no data on nearby commercial or recreational fish catches. and Sherwood, 2004), and over the past ten years, the estuary has Instead, this study specifically investigated the influence of estuarine been artificially opened between June and August due to public outflow on different aspects of coastal sediments. Previous studies pressure from the rising river inundating adjoining farmland and (Barton, 2006; Pope, 2006; Sherwood et al., 2008) have shown that other public amenities (Arundel, 2003; Barton and Sherwood, the estuaries investigated in this study and others along the Victorian 2004). The Anglesea estuary (14411 028"E, 3824059"S) catchment coastline are nutrient rich and so this study focused on the influence covers an area of w125 km2 and is much shorter than the Curdies of estuary outflow on sediment organic matter, microphytobenthos estuary (length approximately 3.5 km; (Sherwood et al., 2008)).