Conceptual Models of Australia's Estuaries and Coastal Waterways : Applications for Coastal Resource Management

This document represents part of Geoscience Australia's contribution to the National Estuaries Assessment and Management (NE) project, Theme 5 (Assessment and Monitoring), Task 5A 'Conceptual Models of Australian Estuaries and Coastal Waterways'. The report contains comprehensive conceptual models of the biophysical processes that operate in a wide range of estuaries and coastal waterways found around Australia.

Geomorphic conceptual models have been developed for each of the seven types of Australian estuaries and coastal waterways. Each conceptual model comprises a three-dimensional block diagram depicting detailed summaries of the structure, evolutionary characteristics, and geomorphology of each coastal waterway type, which are ?overlain? by flow diagrams that depict some of the important biotic and abiotic processes, namely: hydrology, sediment dynamics, and nutrient dynamics. Geomorphology was used as the common 'base layer' in the conceptual models, because sediment is the fundamental, underlying substrate upon which all other estuarine processes depend and operate.

In the conceptual models, wave-dominated systems are depicted as having a relatively narrow entrance that restricts marine flushing, and low water-column turbidity except during extreme events. Tide-dominated systems feature relatively wide entrances, which likely promote efficient marine flushing, very large relative areas of intertidal habitats, and naturally high turbidity due to strong turbulence induced by tidal currents. Strong evidence exists suggesting that estuaries (both wave- and tide-dominated) are the most efficient 'traps' for terrigenous and marine sediments, and these are depicted as providing the most significant potential for trapping and processing of terrigenous nutrient loads. Intertidal areas, such as mangroves and saltmarshes, and also the central basins of wave-dominated estuaries and coastal lagoons, are likely to accumulate the majority of trapped sediments and nutrients.

Conceptual model diagrams, with overlays representing environmental processes, can be used as part of a decision support system for environmental managers, and as a tool for comparative assessment in which a more integrative and shared vision of the relationship between components in an ecosystem can be applied.

本文件为澳大利亚地球科学局（Geoscience Australia）参与国家河口评估与管理（National Estuaries Assessment and Management，NE）项目的成果之一，具体对应第五主题「评估与监测」下的5A任务「澳大利亚河口与沿海水道概念模型」。本报告系统梳理并呈现了澳大利亚境内各类河口与沿海水道中所发生的生物物理过程（biophysical processes）的完整概念模型。

研究团队针对澳大利亚的7类河口与沿海水道分别构建了地貌概念模型（geomorphic conceptual models）。每一类概念模型均包含三维立体框图，用以详细阐述对应沿海水道类型的结构、演化特征与地貌学（geomorphology）特征；此类模型之上还叠加了流程示意图，用以展示若干关键的生物与非生物过程，具体包括水文过程、沉积物动力学（sediment dynamics）与营养盐动力学（nutrient dynamics）。由于沉积物是所有河口过程赖以开展的基础性底层基质，因此地貌学被作为概念模型的通用「基础层」。

在本概念模型中，波浪主控型系统被描述为拥有相对狭窄的河口，该河口会限制海水交换（marine flushing），且除极端事件外水体浊度（water-column turbidity）较低。潮汐主控型系统则以相对宽阔的河口为特征，此类河口可促进高效的海水交换，拥有占比极高的潮间带生境（intertidal habitats），且因潮流引发的强烈湍流而自然呈现较高浊度。现有充分证据表明，无论是波浪主控型还是潮汐主控型河口，均为陆源（terrigenous）与海洋沉积物最高效的「汇」；同时，这类系统也被认为具备截留与处理陆源营养盐负荷的最强潜力。潮间带区域（如红树林与盐沼），以及波浪主控型河口与沿海潟湖的中央盆地，大概率会积累绝大多数被截留的沉积物与营养盐。

带环境过程叠加层的概念模型图，可作为环境管理者决策支持系统的组成部分，同时也可作为比较评估工具，用于构建对生态系统各组分间关系更具整体性与共识性的认知框架。