Potential Groundwater Dependent Ecosystem (GDE) Mapping for the East Gippsland CMA

Potential Groundwater Dependent Ecosystems (GDE) are ecosystems identified within the landscape as likely to be at least partly dependent on groundwater. State-wide screening analysis was performed to identify locations of potential terrestrial GDEs, including wetland areas. The GDE mapping was developed utilising satellite remote sensing data, geological data and groundwater monitoring data in a GIS overlay model. Validation of the model through field assessment has not been performed. The method has been applied for all of Victoria and is the first step in identifying potential groundwater dependent ecosystems that may be threatened by activities such as drainage and groundwater pumping. The dataset specifically covers the East Gippsland Catchment Management Authority (CMA) area. The method used in this research is based upon the characteristics of a potential GDE containing area as one that:\n1. Has access to groundwater. By definition a GDE must have access to groundwater. For GDE occurrences associated with wetlands and river systems the water table will be at surface with a zone of capillary extension. In the case of terrestrial GDE's (outside of wetlands and river systems), these are dependent on the interaction between depth to water table and the rooting depth of the vegetation community.\n2. Has summer (dry period) use of water. Due to the physics of root water uptake, GDEs will use groundwater when other sources are no longer available; this is generally in summer for the Victorian climate. The ability to use groundwater during dry periods creates a contrasting growth pattern with surrounding landscapes where growth has ceased.\n3. Has consistent growth patterns, vegetation that uses water all year round will have perennial growth patterns.\n4. Has growth patterns similar to verified GDEs. \nThe current mapping does not indicate the degree of groundwater dependence, only locations in the landscape of potential groundwater dependent ecosystems. This dataset does not directly support interpretation of the amount of dependence or the amount of groundwater used by the regions highlighted within the maps. Further analysis and more detailed field based data collection are required to support this.\n\nThe core data used in the modelling is largely circa 1995 to 2005. It is expected that the methodology used will over estimate the extent of terrestrial GDEs. There will be locations that appear from EvapoTranspiration (ET) data to fulfil the definition of a GDE (as defined by the mapping model) that may not be using groundwater. Two prominent examples are: 1. Riparian zones along sections of rivers and creeks that have deep water tables where the stream feeds the groundwater system and the riparian vegetation is able to access this water flow, as well as any bank storage contained in the valley alluvials. 2. Forested regions that are accessing large unsaturated regolith water stores.\nThe terrestrial GDE layer polygons are classified based on the expected depth to groundwater (ie shallow 5 m). Additional landscape attributes are also assigned to each mappnig polygon.\n\nIn 2011-2012 a species tolerance model was developed by Arthur Rylah Institute, collaborating with DPI, to model landscapes with ability to support GDEs and to provide a relative measure of sensitivity of those ecosystems to changes in groundwater availability and quality. Rev 1 of the GDE mapping incorporates species tolerance model attributes for each potential GDE polygon and attributes for interpreted depth to groundwater.\n\nSeparate datasets and associated metadata records have been created for GDE species tolerance.

潜在地下水依赖型生态系统（Potential Groundwater Dependent Ecosystems，GDE）指景观中被识别为可能至少部分依赖地下水的生态系统。已开展全州范围的筛选分析，以识别潜在陆地GDE的分布位置，包括湿地区域。GDE制图通过GIS叠加模型，整合卫星遥感数据、地质数据及地下水监测数据构建而成。尚未通过实地评估对该模型进行验证。该方法已应用于维多利亚州全境，是识别可能受排水、地下水抽取等活动威胁的潜在地下水依赖型生态系统的第一步。该数据集具体覆盖东吉普斯兰集水区管理局（East Gippsland Catchment Management Authority，CMA）区域。

本研究采用的方法基于潜在GDE分布区域的以下特征：
1. 可获取地下水。根据定义，GDE必须能够获取地下水。对于与湿地和河流系统相关的GDE而言，地下水位将处于地表，且存在毛细管延伸带；对于陆地GDE（湿地与河流系统之外），其依赖程度取决于地下水位深度与植被群落根系深度之间的相互作用。
2. 夏季（干旱期）需用水。由于根系吸水的物理特性，当其他水源不可用时，GDE会利用地下水——在维多利亚州气候条件下，这一时期通常为夏季。干旱期利用地下水的能力使其生长模式与周围已停止生长的景观形成鲜明对比。
3. 生长模式稳定。全年需水的植被具有多年生生长模式。
4. 生长模式与已验证GDE相似。

当前制图未标明地下水依赖程度，仅呈现景观中潜在地下水依赖型生态系统的分布位置。该数据集无法直接支持对地图中高亮区域的依赖程度或地下水使用量的解读，需通过进一步分析及更详细的实地数据采集予以支撑。

建模所用核心数据主要为1995年至2005年期间的数据。预计所用方法会高估陆地GDE的分布范围。部分区域根据蒸散（EvapoTranspiration，ET）数据看似符合GDE的定义（按制图模型定义），但实际上可能并未利用地下水。两个典型例子如下：1. 部分河段及溪段的河岸带，其地下水位较深，溪流为地下水系统补给水源，河岸植被可获取该水流及河谷冲积层中的岸存储水；2. 可利用大量非饱和风化层储水的森林区域。

陆地GDE图层多边形根据预期地下水位深度（如浅于5米）进行分类。每个制图多边形还被赋予额外的景观属性。

2011-2012年，Arthur Rylah研究所与DPI合作开发了物种耐受性模型，用于模拟能够支撑GDE的景观，并提供这些生态系统对地下水可获得性及质量变化敏感性的相对度量。GDE制图第1版整合了每个潜在GDE多边形的物种耐受性模型属性及解释性地下水位深度属性。

已针对GDE物种耐受性创建独立数据集及相关元数据记录。