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关于湿地的定义其实有很多种
WHAT IS A WETLAND?
Simply stated, wetlands are parts of our landscape that are defined by the presence of water. More specifically, wetlands are areas where the presence of water determines or influences most, if not all, of an areas biogeochemistry—that is, the biological, physical, and chemical characteristics of a particular site.
简单地说，湿地是我们景观的一部分，由水的存在来定义。更具体地说，湿地是指水的存在决定或影响一个区域生物地球化学的大部分（如果不是全部的话）的区域，即特定地点的生物、物理和化学特征。
Many wetlands are transitional zones between upland and aquatic ecosystems, although others are scattered across the landscape in upland depressions that collect water or in zones where groundwater comes to the surface.
许多湿地是高地和水生生态系统之间的过渡地带，尽管其他湿地分散在收集水的高地洼地或地下水到达地表的区域。
The amount of water present in a wetland can vary greatly. Some wetlands are permanently flooded, while others are only seasonally flooded but retain saturated soils throughout much of the unflooded period. Still other wetlands may rarely flood, but saturated soil conditions still are present long enough to support wetland-adapted plants and for hydric soil characteristics to develop. Hydric soils develop when chemical changes take place in the soil due to the low-oxygen conditions associated with prolonged saturation.
湿地中的水量差异巨大。一些湿地被永久性淹没，而另一些湿地只是季节性淹没，但在大部分未淹没期间维持着水饱和的土壤。还有一些湿地可能很少发生洪水，但饱和土壤条件仍然存在足够长的时间，以支持湿地适宜性植物生长，并发展水成土壤特性。由于与长期饱和相关的低氧条件，当土壤中发生化学变化时，就会形成水成土。
Different plant communities may be found in different types of wetlands, with each species adapted to the local hydrology (the quantity, distribution, and movement of water throughout a given area). Wetland plants are often referred to as hydrophytes because they are specially adapted to grow in saturated soils. Many bird, insect, and other wildlife species are completely dependent on wetlands for critical stages in their life cycles, while many other species make use of wetlands for feeding, resting, or other life activities.
在不同类型的湿地中可能会发现不同的植物群落，每个物种都适应当地的水文条件（特定区域的水量、分布和水流）。湿地植物通常被称为水生植物，因为它们特别适合在饱和土壤中生长。许多鸟类、昆虫和其他野生动物物种在生命周期的关键阶段完全依赖湿地，而许多其他物种则利用湿地进行觅食、休息或其他生命活动。
湿地分类的角度启示：被水淹没的频率 但是季节性被水淹没的地方也可能是洪水的淹没区域 所以应该是未被水淹期间土壤水保和
DEFINING WETLANDS
Although we can readily describe wetland characteristics and what they do, there has been a lot of discussion over how to specifically define what constitutes a wetland. A workable definition became critical in classifying habitat for legal purposes, especially in determining which lands are protected by state and federal legislation. The U.S. Fish and Wildlife Service defined wetlands as follows in 1979:
虽然我们可以很容易地描述湿地的特征以及它们的作用，但是关于如何具体定义湿地的构成，已经有很多讨论。在为法律目的对栖息地进行分类时，一个可行的定义变得至关重要，尤其是在确定哪些土地受州和联邦立法保护时。1979年，美国鱼类和野生动物服务局对湿地的定义如下：
Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface, or the land is covered by shallow water. . . . Wetlands must have one or more of the following three attributes: 1) at least periodically, the land supports predominantly hydrophytes; 2) the substrate is predominantly undrained hydric soil; and 3) the substrate is saturated with water or covered by shallow water at some time during the growing season of each year.
湿地是陆地和水生系统之间的过渡地带，地下水位通常位于或接近地表，或者土地被浅水覆盖。湿地必须具有以下三个属性中的一个或多个：1）至少周期性地，土地主要支持水生植物；2） 基质主要是不排水的水成土；3）在每年生长季节的某个时候，基质被水饱和或被浅水覆盖。
来自湿地遥感书籍中的一些定义：
TYPES OF WETLANDS
There are many different types of wetlands, each determined by its hydrology, water chemistry, soils, and the plant species found there. Wetlands may be characterized as dominated by trees, shrubs, or herbaceous vegetation. They may be fed by precipitation, runoff, or groundwater, with water chemistry ranging from very acidic to alkaline. Below are some of the major wetland types found in the Upper Midwest.
有许多不同类型的湿地，每一种都取决于其水文、水化学、土壤和在那里发现的植物种类。湿地的特征可能是以树木、灌木或草本植物为主。它们可能由降水、径流或地下水补给，水化学性质从酸性到碱性不等。
参考链接：
What Is a Wetland? — The Wetlands Initiative
