Potential Groundwater Dependent Ecosystem (GDE) Mapping for the West 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 West 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:1. 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.2. 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.3. Has consistent growth patterns, vegetation that uses water all year round will have perennial growth patterns.4. Has growth patterns similar to verified GDEs. The 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.The 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.The 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.In 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.Separate datasets and associated metadata records have been created for GDE species tolerance.

潜在依赖地下水生态系统（Groundwater Dependent Ecosystems，GDE）指在地表景观中被识别出的、至少部分依赖地下水的生态系统。本次研究开展了全州范围的筛查分析，以识别潜在陆地型GDE的分布点位，涵盖湿地区域。本次GDE制图依托卫星遥感数据、地质数据与地下水监测数据，通过地理信息系统（Geographic Information System，GIS）叠加模型完成构建，尚未通过实地评估对该模型进行验证。
该方法已覆盖维多利亚州全域，是识别潜在依赖地下水生态系统的首要步骤——此类生态系统可能受到排水、地下水抽取等人类活动的威胁。本数据集特指覆盖西吉普斯兰流域管理局（West Gippsland Catchment Management Authority，CMA）的辖区范围。
本研究采用的方法，基于潜在GDE分布区域的四项核心判定特征：
1. 具备地下水获取途径。根据定义，GDE必须能够获取地下水。对于与湿地、河流系统相关的GDE而言，其地下水位将处于地表，且存在毛细上升带。而陆地型GDE（湿地与河流系统以外的区域）的地下水获取能力，则取决于地下水位埋深与植被群落根系深度之间的相互作用。
2. 会在夏季（旱季）取用地下水。受根系吸水的物理特性影响，当其他水源枯竭时，GDE将转而取用地下水——在维多利亚州的气候条件下，这一时段通常为夏季。这类生态系统在旱季仍可获取地下水的特性，使其生长模式与周边已停止生长的景观形成显著差异。
3. 具备持续稳定的生长模式。全年稳定取水的植被将呈现多年生生长特征。
4. 生长模式与已验证的GDE一致。
当前的制图结果仅能标识景观中潜在GDE的分布点位，无法体现其地下水依赖程度。本数据集无法直接解读地图中标注区域的地下水依赖程度或其取用的地下水量，需开展进一步分析与更细致的实地数据采集工作，方能支撑此类解读。
建模所用的核心数据时段大致为1995年至2005年。预计该方法会高估陆地型GDE的分布范围：部分区域从蒸散（EvapoTranspiration，ET）数据来看符合GDE的制图模型定义，但实际上可能并未取用地下水。典型案例包括两类：
1. 部分河流与溪谷沿岸的滨水带，其地下水位较深，但溪流可补给地下水系统，滨水植被既可以获取该水流，也可利用河谷冲积层中的岸堤储水。
2. 依赖大型非饱和风化层储水的林区。
陆地型GDE图层的面要素多边形，依据预期地下水位埋深进行了分类（例如浅埋深≤5米）。每个制图多边形还被赋予了额外的景观属性。
2011-2012年，亚瑟·里尔研究所（Arthur Rylah Institute）与DPI合作开发了物种耐受模型，用于对可支撑GDE的景观进行建模，并为这些生态系统对地下水可用性与水质变化的敏感性提供相对量化指标。GDE制图的修订版1（Rev 1）纳入了每个潜在GDE多边形的物种耐受模型属性，以及解译得到的地下水位埋深属性。
针对GDE物种耐受模型，已创建了独立的数据集及相关元数据记录。