chapter  18
26 Pages

1Chapter 8 Structure and Function of Warm Temperate East Australian Coastal Lagoons: Implications for Natural and Anthropogenic Changes

Abstract .......................................................................................................................................... 458 18.1 Introduction ......................................................................................................................... 458 18.2 Study Area........................................................................................................................... 459

18.2.1 Geomorphic Evolution ............................................................................................459 18.2.2 Climate ....................................................................................................................462 18.2.3 Catchment Characteristics/Land Use/Stressors ...................................................... 462

18.3 Water and Sediment Quality ...............................................................................................465 18.4 Benthic Habitats ..................................................................................................................465 18.5 Carbon Budgets ...................................................................................................................469 18.6 Wild Fisheries Production ................................................................................................... 473 18.7 Implications for Natural and Anthropogenic Change ......................................................... 476

18.7.1 Natural Change ....................................................................................................... 476 18.8 Pollutant Loads ................................................................................................................... 476 18.9 Acidification, Deoxygenation, and Fish Kills ..................................................................... 476 18.10 Climate Change Impacts ..................................................................................................... 477

18.10.1 Sea Level Rise .......................................................................................................477 18.10.2 Temperature ..........................................................................................................477 18.10.3 Rainfall and Runoff ..............................................................................................478 18.10.4 Storminess and Wave Climate .............................................................................. 478

18.11 Conclusions ......................................................................................................................... 479 Acknowledgments .......................................................................................................................... 479 References ...................................................................................................................................... 479

Three warm temperate east Australian coastal systems (Wallis Lake, Camden Haven, and Hastings River Estuary) serve as case studies to explore relationships between the structure and function of coastal lagoons. These three systems provide examples of bar-built or wave-dominated estuaries/ coastal lagoons at different stages of maturity (infilling) on the east coast of Australia. Wallis Lake is an immature lagoon with minimal infilling and a large depositional mud basin. Camden Haven Estuary is a semimature lagoon with two partially filled shallow lakes connected by an infilled channelized river system, and the Hastings River Estuary is a mature lagoon with a highly channelized interconnected river system. As these systems evolve (mature), the areal extent of their geomorphic units (structure) changes linearly, with a decrease in the extent of deep and shallow subtidal mud shoals and an increase in extent of marine sand channel and fluvial sands. However, the function trajectory associated with the changes in the structure of these coastal lagoons as they mature show both linear and nonlinear trends. As a coastal lagoon progresses from an immature to a semimature state and the mud basin fills and shallows, there is an increase in the ratio of benthic to pelagic production due to greater light availability and an increase in net ecosystem metabolism (NEM) associated with less organic matter being trapped and respired. With further maturation, a coastal lagoon completely infills, and there is a large decrease in the benthic to pelagic ratio caused by higher turbidity (and less light) and less suitable substrate for benthic producers. This leads to a decrease in NEM due to more organic matter being trapped and respired. Total wild fisheries production (catch per fisher based on 20 years of commercial fish catch) follows a similar nonlinear trend, with maximum production in the semimature Camden Haven. In contrast, the production (catch per fisher) of higher trophic level fish species (i.e., trophic level above 2) shows a linear decrease as the system matures, most likely attributable to less organic matter availability for higher-order production. Immature lagoons are at greatest risk from pollutant loading and climate change impacts (e.g., sea level rise, higher temperatures, increased rainfall and runoff, and greater storminess and wave climate) largely because of poor flushing. In contrast, mature lagoons are at greatest risk from acidification, deoxygenation, and fish kills due to larger alluvial plains.