39 Applications of Remote Sensing and GIS in Wetland Dynamics

Dr. L.T. Sasang Guite

  1. Contents
  • What is a wetland
  • What are the characteristics of wetland
  • What are the basic categories of wetland and which are the commonly found What is its ecological importance
  • Why does wetlands need to study
  • How remote sensing and GIS can help in studding wetland dynamics Which are the commonly use remote sensing data in wetland study
  • Which are the commonly used classification techniques in wetland study

 

 2. Aim of the Module

  • Understand the characteristics and types of wetlands Explain the ecological importance of wetland
  • Explain the use of remote sensing and GIS in study of wetland

 

 3. Introduction

 

Wetlands are the transitional zone between aquatic and terrestrial region. Water covers the soil or present near the surface of the soil all year or for varying periods of time during the year. Wetlands are areas saturated with water, either permanently or seasonally, displaying characteristics of a distinct ecosystem. The wetlands are distinguishes from other land forms or water bodies by their distinct characteristic vegetation type of aquatic plants that are adapted to the unique hydric soil.

 

During rainy season a land that saturate water cannot be considered as wetland due to their temporal characteristic even though the land is wet. Wetlands are characterized as having water saturation for a long period to support aquatic plants. Water saturation largely determines the genesis of soil type development and the types of plant and animal found, thus, supporting both aquatic and terrestrial species. The presence of prolonged water saturation creates conditions that favour the growth of adapted plants (hydrophytes) and wetland (hydric) soils.Wetlands have been identified as ecotones acts as transitional zone between dry land and water.

 

 

2. Characteristics of Wetland

 

Wetlands features a unique characteristic that can be categorized as riverine (that are associated with streams and rivers), lacustrine (that are associated with lakes and reservoirs), and palustrine (which are isolated and are inland type). The sources of water flow into wetlands are predominantly from precipitation, surface water and ground water and the process of water out flow of water by evapo-transpiration, surface runoff and sub-surface water outflow. The hydrodynamics (inflow and out flow of water) affects the hydro-period (temporal fluctuations in water levels) by controlling the water balance and water storage within a wetland.Carbon is the major nutrient cycled within the soil of wetland while sulphur, phosphorus, carbon and nitrogen are also found. Anaerobic and aerobic respiration in the soil of wetland has greatly influenced the nutrient cycling thereby contributing to the chemical variations in water.

 

The biota of wetland includes the vegetation zones and animal population where the important factor affecting is the duration of inundation of land, while factors of fertility and salinity also have same impact on the wetland. In fens, one of the types of wetland, biota is highly dependent on water chemistry, where water flowing into wetlands depends on the source of water and the geological material in which it flows through. As the river or stream flows through organic matter from a higher elevation that drains into the wetland, the biota may vary within the wetland.

 

3. Types of Wetland:

 

There are 42 different categories of wetlands. It broadly classified as;

  • Marine and costal wetland
  • Inland wetland and
  • Man-made wetlands

Another classification can be done depending upon types of dominant water supply or water type, as;

  • Precipitation domain wetland
  • Ground water domain wetland and
  • Surface water domain wetlands.

 

3.1 Precipitation domain wetland

 

This kind of wetland is mostly dominated by rainfall or precipitation. Bog is one of the common example in this type. Bogs are waterlogged peat lands in old lake basins or depressions in the landscape, forming where peat accumulation exceeds decomposition as a result of climatic conditions. These are precipitation dominated because the accumulated peat elevate to such an extent that there are few or no surface inflows thereby resulting into low rates of primary productivity and decomposition as they do not receive organic matter transported by surface water. Typically acidic in nature due to the dominant living plant matter, Sphagnum moss. The pH value can be as low as 3.0 – 4.0 and dissolved oxygen levels vary from ND (non-detectable) to 6 ppm, temperature is also variable (based on location)

 

3.2 Ground water domain wetland

 

This type of wetland is dominated by ground water. Fans are most common in this type. Fens are peat-accumulating wetlands that form at low points in the landscape or near slopes where ground water intercepts the soil surface. Water levels are fairly constant all year because the water supply is provided by ground water inputs. Fens, like bogs, tend to be glacial in origin and are found in the northern United States or on mountains and mountainsides. Fens are dominated by herbaceous plants, such as grasses and sedges, typically lack the Sphagnum moss that predominates in bogs, and look like meadows.Fens may represent an earlier successional stage of peat accumulation than bogs, and over geologic time, fens may become bogs. Unlike bogs, fens receive minerals and nutrients from ground water, because they have built up less peat and ground water is still sufficiently close to the surface. Fens are less acidic than bogs because they have little or no Sphagnum, and because ground water inputs tend to be neutral or alkaline. The pH of fens ranges from 4.0 – 8.0. Dissolved oxygen levels typically vary from 2 ppm to 8 ppm. Hardness ranges from 40 ppm to 95 ppm (based on soil/rock type in area). Temperature ranges from 50 degrees Fahrenheit to 57 degrees Fahrenheit (because of groundwater contact).

Another type is prairie potholes. It is shallow marshlike ponds formed in glacial depressions (such as kettles and depressions near moraines). Range from New York to Montana. It has high groundwater levels. Dissolved oxygen levels typically vary from 3 ppm to 7 ppm. Hardness ranges from 30 ppm to 80 ppm (based on soil/rock type in area). Temperature ranges from 50 degrees F to 57 degrees F (if fed by groundwater).

 

3.3 Surface water domain wetlands:

 

These types of wetland are primarily saturated by surface water. Marshes are most common type of wetland in this category. Marshes are one of the broadest categories of wetlands and in general harbour the greatest biological diversity. They are characterized by shallow water, little or no peat deposition, and mineral soils. Marshes are dominated by floating-leafed plants (such as water lilies and duckweed) or emergent soft-stemmed aquatic plants (such as cattails, arrowheads, reeds, and sedges). Marshes form in depressions in the landscape, as fringes around lakes, and along slow-flowing streams and rivers. They are the transition between land and water. pH levels are 5 to 8. High groundwater, levels. Dissolved oxygen levels typically vary from 3 ppm to 10 ppm. Hardness based on soil/rock type in area. Temperature also is variable (based on location).

 

Tidal marsh is a continually or frequently inundated salt water wetland dominated by herbaceous vegetation that are typically shallow in nature and form in the transitional areas between land and water (surrounding salt water bays, mouths of rivers or tidal pool areas). The pH levels ranges between 6 to 8 and dissolved oxygen levels typically vary from 3 ppm to 10 ppm. Another is the Tidal freshwater marshes that are found in the upstream of estuaries where tides influence the water levels. Though, this type is predominantly fresh as it receives substantial water and nutrients from upstream water resources, as well as inputs from surface runoff and precipitation. The high level of nutrient inputs due to abundant sources it contributes to extreme high primary productivity and biodiversity.

 

4. Ecological importance of wetland:

 

The ecological importances of Wetlands are numerous as they significantly contribute in water purification, flood control, carbon sink and shoreline stability and so on. The wetland ecosystem is considered as the most biologically diverse of all ecosystems that serves asylum to wide species of plant and animal life. Some of the wetlands are constructed or man-made those are used to treat municipal and industrial wastewater. In urban modelling wetland thus play a role in water-sensitive urban design. Thus the ecological importance ranges from not only maintaining the biotic environment but also in many urban design and occur naturally on every continent, the largest including the Amazon River basin, the West Siberian Plain, and the Pantanal in South America.

 

 

Wetlands are very much productive areas that perform essential ecological function. Wetland benefits include providing wildlife habitat, controlling erosion and conserving and purifying water. Wetland provides habitat for a diverse assortment of wildlife species. These include birds, mammals, amphibians, fish, invertebrates and plants. Healthy wetlands are essential to the survival of many of these species. Wetlands are the areas of where land and water meet. For wildlife, this translates into rich habitat with an abundance of food and protective cover. The wetland edge or riparian zone is a transition zone between wetland and upland. Healthy riparian zones are diversehabitat that attracts non aquatic wildlife including many species of songbirds and upland mammals like the red fox.

 

Wetlands are natural water purifiers. Wetland vegetation helps maintain water quality by breaking down and assimilating contaminates carried by surface run off. Wetland purifies water through a numbers of biological, chemical and physical processes. Wetland stores surface water. Wetlands functions like sponges by soaking up excess water during spring freshets. This reduces the impact of the flooding on upland areas. It slows and stabilize heavy surface run off. This reduces erosion of stream banks and flood plain areas and allows a portion of the sediments carried by run off to settle. Areas downstream benefit from a reduce rate of sediment deposition.

 

5.   Role of Remote sensing and GIS in wetland dynamics:

 

Wetland comprise only three to six present of earth’s land surface area, but they provide human population with a host of goods and services, including water quality, agricultural production, fisheries and recreation. A wetland needs to be monitored over time period in order to assess the functioning that are as per ecologically sustainable level or degrading. Degraded wetlands will result in loss of water quality, threatened the existence of species and poor soil conditions.

 

Thus the geo-informatics mainly remote sensing and GIS is playing a significant role in monitoring and restoring of wetland. As for the dynamics of lake in Egypt were studied using multi temporal satellite remote sensing data, analysing with the help of digital image processing techniques and GIS overlay analysis. The hydrological parameters also assess with the help of GIS technique for suggest suitable mitigation plans as waste water treatment, improvement of ground water quality and long term monitoring of water storage capacity for restoration. Similarly the impact of land use / land cover dynamics and hydrological variability was analysed and action plan was developed for its conservation in India using geospatial techniques.

 

 

Traditionally Landsat MSS, Landsat TM, Landsat ETM+ and SPOT satellite system have been used to study wetlands. Other studied have been including AVHRR, IRS, JERS-1, ERS-1 SIR-C and Radarsat. There are limitations in use of optical data regarding wetland mapping. But in recent years multispectral IKONOS and QuickBird data, with spatial resolutions of 4 by 4 m (13 by 13 ft) and 2.44 by 2.44 m (8.0 by 8.0 ft), respectively, have provided with excellent data source.

 

As far the classification of these images is concerned most of the earliest work includes visual interpretation with the help of aerial photography. Unsupervised classificationor clustering is the most commonly used digital classification to map of wetlands. Another commonly used method is maximum Likelihood algorithm with a supervised classification.

 

But most of the time these classification represents low to average accuracy in relation to ground. To increase the accuracy researches developed and apply some other methods as;

 

  1. Using multi temporal data with various GIS analysis tools.
  2. Non parametric classification such as rule base classification (using multi spectral imagery).

 

One of the most important facts is that wetlands could be better defined on imagery acquired in spring when the water level is high but not flooded. Seasonal variation one of the important consideration concerning the water body as well as surrounding land use land cover.

 

 

Some of the other methods can be used as:

 

a. Using multi sensor assessment

  1. Neural network
  2. Hyper spectral data
  3. Ancillary data

 

Ancillary data provides the solution of the problem that is differentiate between spectral similarities in wetland and agricultural land with water and forest water logged areas. Notwithstanding the limitations with image acquisition, the wetlands study have many challenges as obtaining data is often linked to other purposes such as the analysis of land cover or land use and also natural wetlands are difficult to monitor as areas are often difficult to access that requires exposure to native wildlife and potential endemic disease.

 

Why wetlands?

Wetland provides the important fundamental ecological services

Wetland regulates water regimes and are sources of biodiversity at all levels-species genetic and ecosystem.

Wetlands resource provides a great economic scientific, cultural and recreational value for the community

Wetland study becomes important in accessing encroachment of wetlands by anthropogenic factor

Regarding wetland, the user of geospatial techniques like remote sensing and GIS, user primary concern is to monitor the wetlands and assess the changes within the wetland and its surrounding areas to take possible mitigation plans to conserve the wetlands in all manners. Considering the importance of wetland as mentioned above and its dynamic nature, remote sensing and GIS are very much useful tools to monitor the sites.

 

6.   Reference:

  • Arnoff, S. (1989),Geographical Information Systems: A Management Perspective, WDL Publications, Canada Narayan, L.R.A., (2001), Remote Sensing and its application, University Press, Hyderabad.
  • Schultz, G.A. &Engman, E.T. (2000), Remote Sensing in hydrology and water management, Springer-Verlang, Berlin, Germany
  • Space application centre, Ahmadabad, (2010): National wetland Atlas
  • SAC/EPSA/ABHG/NWIA/ATLAS/28/2010, Ministry of Environment and Forest